Fix doc generation when NamedSplit is used as parameter default value

Fix doc generation when `NamedSplit` is used as parameter default value.

Fix #7035.

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_7036). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

<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) | 0.005582 / 0.011353 (-0.005771) | 0.003968 / 0.011008 (-0.007041) | 0.063672 / 0.038508 (0.025164) | 0.032360 / 0.023109 (0.009251) | 0.241351 / 0.275898 (-0.034547) | 0.264926 / 0.323480 (-0.058554) | 0.003186 / 0.007986 (-0.004800) | 0.003423 / 0.004328 (-0.000906) | 0.049600 / 0.004250 (0.045350) | 0.045558 / 0.037052 (0.008506) | 0.253326 / 0.258489 (-0.005163) | 0.289474 / 0.293841 (-0.004367) | 0.030285 / 0.128546 (-0.098261) | 0.012424 / 0.075646 (-0.063222) | 0.203914 / 0.419271 (-0.215358) | 0.036569 / 0.043533 (-0.006964) | 0.245252 / 0.255139 (-0.009887) | 0.261971 / 0.283200 (-0.021228) | 0.018276 / 0.141683 (-0.123406) | 1.120386 / 1.452155 (-0.331769) | 1.181736 / 1.492716 (-0.310980) |

### 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) | 0.095427 / 0.018006 (0.077421) | 0.300666 / 0.000490 (0.300176) | 0.000205 / 0.000200 (0.000005) | 0.000045 / 0.000054 (-0.000009) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.019255 / 0.037411 (-0.018156) | 0.062645 / 0.014526 (0.048119) | 0.074822 / 0.176557 (-0.101734) | 0.121222 / 0.737135 (-0.615913) | 0.076136 / 0.296338 (-0.220202) |

### 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) | 0.279756 / 0.215209 (0.064547) | 2.769680 / 2.077655 (0.692025) | 1.466156 / 1.504120 (-0.037964) | 1.348337 / 1.541195 (-0.192857) | 1.348311 / 1.468490 (-0.120179) | 0.710414 / 4.584777 (-3.874363) | 2.379192 / 3.745712 (-1.366520) | 2.990227 / 5.269862 (-2.279635) | 1.909749 / 4.565676 (-2.655928) | 0.079677 / 0.424275 (-0.344598) | 0.005116 / 0.007607 (-0.002491) | 0.335442 / 0.226044 (0.109398) | 3.308757 / 2.268929 (1.039828) | 1.831681 / 55.444624 (-53.612944) | 1.528642 / 6.876477 (-5.347835) | 1.554577 / 2.142072 (-0.587496) | 0.777722 / 4.805227 (-4.027505) | 0.132164 / 6.500664 (-6.368501) | 0.042277 / 0.075469 (-0.033193) |

### 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) | 0.964461 / 1.841788 (-0.877327) | 11.436569 / 8.074308 (3.362261) | 9.801367 / 10.191392 (-0.390025) | 0.130214 / 0.680424 (-0.550210) | 0.015288 / 0.534201 (-0.518913) | 0.303992 / 0.579283 (-0.275292) | 0.258128 / 0.434364 (-0.176236) | 0.347259 / 0.540337 (-0.193078) | 0.438156 / 1.386936 (-0.948780) |

</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) | 0.006019 / 0.011353 (-0.005334) | 0.003872 / 0.011008 (-0.007136) | 0.050763 / 0.038508 (0.012255) | 0.033993 / 0.023109 (0.010884) | 0.271789 / 0.275898 (-0.004109) | 0.298849 / 0.323480 (-0.024631) | 0.004486 / 0.007986 (-0.003500) | 0.002789 / 0.004328 (-0.001540) | 0.049926 / 0.004250 (0.045676) | 0.040470 / 0.037052 (0.003418) | 0.287533 / 0.258489 (0.029044) | 0.320066 / 0.293841 (0.026225) | 0.033039 / 0.128546 (-0.095508) | 0.011842 / 0.075646 (-0.063804) | 0.061016 / 0.419271 (-0.358256) | 0.034807 / 0.043533 (-0.008726) | 0.272079 / 0.255139 (0.016940) | 0.291603 / 0.283200 (0.008403) | 0.018676 / 0.141683 (-0.123007) | 1.171214 / 1.452155 (-0.280940) | 1.210691 / 1.492716 (-0.282025) |

### 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) | 0.093045 / 0.018006 (0.075038) | 0.301045 / 0.000490 (0.300556) | 0.000213 / 0.000200 (0.000013) | 0.000052 / 0.000054 (-0.000003) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.022616 / 0.037411 (-0.014795) | 0.077271 / 0.014526 (0.062746) | 0.088959 / 0.176557 (-0.087598) | 0.129961 / 0.737135 (-0.607174) | 0.090495 / 0.296338 (-0.205843) |

### 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) | 0.301864 / 0.215209 (0.086655) | 2.947486 / 2.077655 (0.869831) | 1.587123 / 1.504120 (0.083003) | 1.453799 / 1.541195 (-0.087396) | 1.474296 / 1.468490 (0.005806) | 0.718609 / 4.584777 (-3.866168) | 0.948426 / 3.745712 (-2.797286) | 2.877275 / 5.269862 (-2.392586) | 1.930940 / 4.565676 (-2.634736) | 0.079207 / 0.424275 (-0.345068) | 0.005379 / 0.007607 (-0.002228) | 0.357969 / 0.226044 (0.131925) | 3.576455 / 2.268929 (1.307527) | 1.985058 / 55.444624 (-53.459566) | 1.663730 / 6.876477 (-5.212747) | 1.812752 / 2.142072 (-0.329320) | 0.800200 / 4.805227 (-4.005027) | 0.135124 / 6.500664 (-6.365540) | 0.041211 / 0.075469 (-0.034258) |

### 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) | 1.032394 / 1.841788 (-0.809394) | 12.082436 / 8.074308 (4.008128) | 10.198703 / 10.191392 (0.007311) | 0.143578 / 0.680424 (-0.536846) | 0.015576 / 0.534201 (-0.518625) | 0.301450 / 0.579283 (-0.277833) | 0.126596 / 0.434364 (-0.307768) | 0.339437 / 0.540337 (-0.200900) | 0.445454 / 1.386936 (-0.941482) |

</details>
</details>

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