[docs] Custom decoding transforms

Adds custom decoding transform solution to the docs to fix #5782.

Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_5836). All of your documentation changes will be reflected on that endpoint.

The error seems unrelated to the changes, so feel free to merge.

<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.006562 / 0.011353 (-0.004791) | 0.004568 / 0.011008 (-0.006440) | 0.098151 / 0.038508 (0.059643) | 0.028117 / 0.023109 (0.005008) | 0.305442 / 0.275898 (0.029544) | 0.338288 / 0.323480 (0.014808) | 0.005012 / 0.007986 (-0.002973) | 0.003415 / 0.004328 (-0.000913) | 0.075022 / 0.004250 (0.070771) | 0.036869 / 0.037052 (-0.000183) | 0.301427 / 0.258489 (0.042937) | 0.348485 / 0.293841 (0.054644) | 0.030761 / 0.128546 (-0.097785) | 0.011461 / 0.075646 (-0.064185) | 0.321987 / 0.419271 (-0.097285) | 0.042885 / 0.043533 (-0.000648) | 0.300691 / 0.255139 (0.045552) | 0.333208 / 0.283200 (0.050008) | 0.090203 / 0.141683 (-0.051480) | 1.459744 / 1.452155 (0.007590) | 1.522960 / 1.492716 (0.030243) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.213219 / 0.018006 (0.195213) | 0.408118 / 0.000490 (0.407629) | 0.003716 / 0.000200 (0.003516) | 0.000077 / 0.000054 (0.000022) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.023060 / 0.037411 (-0.014351) | 0.097423 / 0.014526 (0.082897) | 0.103988 / 0.176557 (-0.072568) | 0.162793 / 0.737135 (-0.574343) | 0.108282 / 0.296338 (-0.188056) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.431628 / 0.215209 (0.216419) | 4.300881 / 2.077655 (2.223226) | 2.058853 / 1.504120 (0.554733) | 1.897910 / 1.541195 (0.356715) | 1.991723 / 1.468490 (0.523233) | 0.699686 / 4.584777 (-3.885091) | 3.395004 / 3.745712 (-0.350708) | 1.841613 / 5.269862 (-3.428248) | 1.152347 / 4.565676 (-3.413330) | 0.082517 / 0.424275 (-0.341758) | 0.012323 / 0.007607 (0.004715) | 0.535812 / 0.226044 (0.309767) | 5.374103 / 2.268929 (3.105174) | 2.429662 / 55.444624 (-53.014962) | 2.097199 / 6.876477 (-4.779277) | 2.172625 / 2.142072 (0.030552) | 0.810156 / 4.805227 (-3.995071) | 0.151629 / 6.500664 (-6.349035) | 0.066528 / 0.075469 (-0.008941) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.220667 / 1.841788 (-0.621121) | 13.696976 / 8.074308 (5.622668) | 14.042916 / 10.191392 (3.851524) | 0.129626 / 0.680424 (-0.550798) | 0.016593 / 0.534201 (-0.517607) | 0.383747 / 0.579283 (-0.195536) | 0.386872 / 0.434364 (-0.047492) | 0.456524 / 0.540337 (-0.083813) | 0.545033 / 1.386936 (-0.841903) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.006361 / 0.011353 (-0.004992) | 0.004516 / 0.011008 (-0.006493) | 0.077155 / 0.038508 (0.038647) | 0.027239 / 0.023109 (0.004130) | 0.359892 / 0.275898 (0.083994) | 0.391994 / 0.323480 (0.068514) | 0.004950 / 0.007986 (-0.003036) | 0.003379 / 0.004328 (-0.000949) | 0.077057 / 0.004250 (0.072806) | 0.039562 / 0.037052 (0.002509) | 0.364244 / 0.258489 (0.105755) | 0.416033 / 0.293841 (0.122192) | 0.031049 / 0.128546 (-0.097497) | 0.011479 / 0.075646 (-0.064167) | 0.086479 / 0.419271 (-0.332793) | 0.039381 / 0.043533 (-0.004151) | 0.372143 / 0.255139 (0.117004) | 0.388569 / 0.283200 (0.105369) | 0.090954 / 0.141683 (-0.050728) | 1.540957 / 1.452155 (0.088802) | 1.596841 / 1.492716 (0.104125) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.221130 / 0.018006 (0.203123) | 0.403728 / 0.000490 (0.403238) | 0.003172 / 0.000200 (0.002972) | 0.000078 / 0.000054 (0.000024) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.024963 / 0.037411 (-0.012449) | 0.101065 / 0.014526 (0.086539) | 0.110846 / 0.176557 (-0.065710) | 0.158578 / 0.737135 (-0.578557) | 0.112235 / 0.296338 (-0.184104) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.457320 / 0.215209 (0.242111) | 4.548094 / 2.077655 (2.470439) | 2.175376 / 1.504120 (0.671256) | 1.964755 / 1.541195 (0.423561) | 2.008128 / 1.468490 (0.539638) | 0.702448 / 4.584777 (-3.882329) | 3.437595 / 3.745712 (-0.308117) | 3.009871 / 5.269862 (-2.259990) | 1.558181 / 4.565676 (-3.007496) | 0.082568 / 0.424275 (-0.341707) | 0.012371 / 0.007607 (0.004764) | 0.550688 / 0.226044 (0.324644) | 5.534210 / 2.268929 (3.265282) | 2.649605 / 55.444624 (-52.795020) | 2.317293 / 6.876477 (-4.559184) | 2.351525 / 2.142072 (0.209453) | 0.808971 / 4.805227 (-3.996256) | 0.152737 / 6.500664 (-6.347927) | 0.068416 / 0.075469 (-0.007053) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.340219 / 1.841788 (-0.501569) | 13.903388 / 8.074308 (5.829080) | 13.063477 / 10.191392 (2.872085) | 0.130216 / 0.680424 (-0.550208) | 0.016522 / 0.534201 (-0.517679) | 0.398946 / 0.579283 (-0.180337) | 0.382450 / 0.434364 (-0.051914) | 0.491007 / 0.540337 (-0.049330) | 0.577747 / 1.386936 (-0.809189) |

</details>
</details>

![](https://cml.dev/watermark.png#15c37ed142e4fbcb8c00ae62d4c71c84ce41959a "CML watermark")


<details>
<summary>Show benchmarks</summary>

PyArrow==8.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.007812 / 0.011353 (-0.003541) | 0.005563 / 0.011008 (-0.005446) | 0.099372 / 0.038508 (0.060864) | 0.035629 / 0.023109 (0.012520) | 0.301457 / 0.275898 (0.025559) | 0.339136 / 0.323480 (0.015656) | 0.006152 / 0.007986 (-0.001834) | 0.005843 / 0.004328 (0.001515) | 0.075280 / 0.004250 (0.071030) | 0.052789 / 0.037052 (0.015736) | 0.301805 / 0.258489 (0.043316) | 0.347918 / 0.293841 (0.054078) | 0.036182 / 0.128546 (-0.092364) | 0.012655 / 0.075646 (-0.062991) | 0.334428 / 0.419271 (-0.084844) | 0.062746 / 0.043533 (0.019213) | 0.296932 / 0.255139 (0.041793) | 0.314115 / 0.283200 (0.030916) | 0.121291 / 0.141683 (-0.020392) | 1.453252 / 1.452155 (0.001097) | 1.564714 / 1.492716 (0.071997) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.243810 / 0.018006 (0.225804) | 0.547129 / 0.000490 (0.546640) | 0.004666 / 0.000200 (0.004466) | 0.000089 / 0.000054 (0.000035) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.028214 / 0.037411 (-0.009197) | 0.108878 / 0.014526 (0.094352) | 0.122313 / 0.176557 (-0.054243) | 0.182412 / 0.737135 (-0.554723) | 0.127014 / 0.296338 (-0.169324) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.423946 / 0.215209 (0.208737) | 4.207112 / 2.077655 (2.129457) | 2.048658 / 1.504120 (0.544538) | 1.843593 / 1.541195 (0.302398) | 1.952426 / 1.468490 (0.483936) | 0.712098 / 4.584777 (-3.872679) | 3.824971 / 3.745712 (0.079258) | 3.507141 / 5.269862 (-1.762721) | 1.868866 / 4.565676 (-2.696810) | 0.087895 / 0.424275 (-0.336380) | 0.012783 / 0.007607 (0.005176) | 0.524087 / 0.226044 (0.298042) | 5.246498 / 2.268929 (2.977570) | 2.495944 / 55.444624 (-52.948680) | 2.126779 / 6.876477 (-4.749698) | 2.315545 / 2.142072 (0.173472) | 0.859546 / 4.805227 (-3.945681) | 0.173457 / 6.500664 (-6.327208) | 0.067483 / 0.075469 (-0.007986) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.173851 / 1.841788 (-0.667937) | 15.091913 / 8.074308 (7.017605) | 14.640035 / 10.191392 (4.448643) | 0.168498 / 0.680424 (-0.511926) | 0.017513 / 0.534201 (-0.516688) | 0.425770 / 0.579283 (-0.153513) | 0.434248 / 0.434364 (-0.000116) | 0.504204 / 0.540337 (-0.036134) | 0.616885 / 1.386936 (-0.770051) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.007775 / 0.011353 (-0.003578) | 0.005153 / 0.011008 (-0.005855) | 0.075461 / 0.038508 (0.036953) | 0.034994 / 0.023109 (0.011885) | 0.372389 / 0.275898 (0.096491) | 0.397911 / 0.323480 (0.074431) | 0.006572 / 0.007986 (-0.001413) | 0.005549 / 0.004328 (0.001220) | 0.075101 / 0.004250 (0.070851) | 0.054014 / 0.037052 (0.016962) | 0.368964 / 0.258489 (0.110475) | 0.425353 / 0.293841 (0.131512) | 0.035546 / 0.128546 (-0.093001) | 0.012707 / 0.075646 (-0.062939) | 0.087418 / 0.419271 (-0.331853) | 0.046425 / 0.043533 (0.002893) | 0.363982 / 0.255139 (0.108843) | 0.376421 / 0.283200 (0.093221) | 0.105369 / 0.141683 (-0.036314) | 1.494408 / 1.452155 (0.042253) | 1.596783 / 1.492716 (0.104067) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.258780 / 0.018006 (0.240773) | 0.533373 / 0.000490 (0.532883) | 0.000432 / 0.000200 (0.000232) | 0.000058 / 0.000054 (0.000003) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.030687 / 0.037411 (-0.006725) | 0.110231 / 0.014526 (0.095705) | 0.123738 / 0.176557 (-0.052819) | 0.171999 / 0.737135 (-0.565137) | 0.127673 / 0.296338 (-0.168665) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.448058 / 0.215209 (0.232849) | 4.459381 / 2.077655 (2.381726) | 2.234020 / 1.504120 (0.729900) | 2.038616 / 1.541195 (0.497421) | 2.123795 / 1.468490 (0.655305) | 0.702664 / 4.584777 (-3.882113) | 3.837133 / 3.745712 (0.091420) | 2.138574 / 5.269862 (-3.131287) | 1.375955 / 4.565676 (-3.189722) | 0.086996 / 0.424275 (-0.337280) | 0.012461 / 0.007607 (0.004854) | 0.557978 / 0.226044 (0.331934) | 5.648613 / 2.268929 (3.379685) | 2.777829 / 55.444624 (-52.666796) | 2.392424 / 6.876477 (-4.484052) | 2.482823 / 2.142072 (0.340750) | 0.851891 / 4.805227 (-3.953336) | 0.171335 / 6.500664 (-6.329329) | 0.065041 / 0.075469 (-0.010428) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.319697 / 1.841788 (-0.522091) | 15.748688 / 8.074308 (7.674380) | 13.397042 / 10.191392 (3.205650) | 0.166424 / 0.680424 (-0.514000) | 0.017755 / 0.534201 (-0.516446) | 0.424989 / 0.579283 (-0.154294) | 0.424705 / 0.434364 (-0.009659) | 0.494190 / 0.540337 (-0.046147) | 0.588315 / 1.386936 (-0.798622) |

</details>
</details>

![](https://cml.dev/watermark.png#15c37ed142e4fbcb8c00ae62d4c71c84ce41959a "CML watermark")