keep more info in DatasetInfo.from_merge #6585

* try not to merge DatasetInfos if they're equal

* fixes losing DatasetInfo during parallel Dataset.map

Comments:
@JochenSiegWork fyi, that seems to also affect the `trainer.push_to_hub()` method, which I guess also needs to parse that DatasetInfo from the `kwargs` used by `push_to_hub`.
There is short discussion about it [here](https://github.com/huggingface/blog/issues/1623).
Would be great if you can check if your PR would also fix that!

> @JochenSiegWork fyi, that seems to also affect the `trainer.push_to_hub()` method, which I guess also needs to parse that DatasetInfo from the `kwargs` used by `push_to_hub`. There is short discussion about it [here](https://github.com/huggingface/blog/issues/1623). Would be great if you can check if your PR would also fix that!

Hi @thiagobarbosa, it might be related but I didn't worked with `push_to_hub` yet. I don't see a minimal example reproducing the specific error in your link. However, if you have a running version producing the error locally you can test it by pulling this PR and run your specific example locally.   

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6586). 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) | 0.004729 / 0.011353 (-0.006624) | 0.002983 / 0.011008 (-0.008025) | 0.062482 / 0.038508 (0.023974) | 0.028406 / 0.023109 (0.005297) | 0.255896 / 0.275898 (-0.020002) | 0.276423 / 0.323480 (-0.047057) | 0.003828 / 0.007986 (-0.004157) | 0.002601 / 0.004328 (-0.001728) | 0.048954 / 0.004250 (0.044704) | 0.040661 / 0.037052 (0.003609) | 0.277710 / 0.258489 (0.019221) | 0.290360 / 0.293841 (-0.003481) | 0.027105 / 0.128546 (-0.101441) | 0.010168 / 0.075646 (-0.065478) | 0.206835 / 0.419271 (-0.212436) | 0.035226 / 0.043533 (-0.008306) | 0.262567 / 0.255139 (0.007428) | 0.273979 / 0.283200 (-0.009221) | 0.017576 / 0.141683 (-0.124106) | 1.125588 / 1.452155 (-0.326566) | 1.185018 / 1.492716 (-0.307698) |

### 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) | 0.092192 / 0.018006 (0.074186) | 0.298350 / 0.000490 (0.297861) | 0.000217 / 0.000200 (0.000017) | 0.000051 / 0.000054 (-0.000003) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.017925 / 0.037411 (-0.019486) | 0.060285 / 0.014526 (0.045759) | 0.076579 / 0.176557 (-0.099978) | 0.118830 / 0.737135 (-0.618305) | 0.073017 / 0.296338 (-0.223322) |

### 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) | 0.288149 / 0.215209 (0.072940) | 2.840004 / 2.077655 (0.762349) | 1.495758 / 1.504120 (-0.008361) | 1.362338 / 1.541195 (-0.178857) | 1.389746 / 1.468490 (-0.078744) | 0.576891 / 4.584777 (-4.007886) | 2.375724 / 3.745712 (-1.369988) | 2.707405 / 5.269862 (-2.562457) | 1.719850 / 4.565676 (-2.845826) | 0.067055 / 0.424275 (-0.357220) | 0.005039 / 0.007607 (-0.002568) | 0.346626 / 0.226044 (0.120581) | 3.468346 / 2.268929 (1.199418) | 1.860686 / 55.444624 (-53.583938) | 1.582929 / 6.876477 (-5.293548) | 1.613131 / 2.142072 (-0.528941) | 0.659022 / 4.805227 (-4.146206) | 0.118477 / 6.500664 (-6.382187) | 0.041614 / 0.075469 (-0.033855) |

### 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) | 1.005062 / 1.841788 (-0.836726) | 11.203210 / 8.074308 (3.128902) | 10.320764 / 10.191392 (0.129372) | 0.128541 / 0.680424 (-0.551883) | 0.014646 / 0.534201 (-0.519555) | 0.285280 / 0.579283 (-0.294003) | 0.263613 / 0.434364 (-0.170751) | 0.321161 / 0.540337 (-0.219177) | 0.420565 / 1.386936 (-0.966371) |

</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) | 0.005288 / 0.011353 (-0.006065) | 0.003048 / 0.011008 (-0.007960) | 0.049196 / 0.038508 (0.010688) | 0.032104 / 0.023109 (0.008994) | 0.279345 / 0.275898 (0.003447) | 0.300194 / 0.323480 (-0.023286) | 0.004045 / 0.007986 (-0.003941) | 0.002594 / 0.004328 (-0.001735) | 0.047680 / 0.004250 (0.043430) | 0.044294 / 0.037052 (0.007241) | 0.292330 / 0.258489 (0.033841) | 0.318610 / 0.293841 (0.024769) | 0.050417 / 0.128546 (-0.078129) | 0.010326 / 0.075646 (-0.065320) | 0.057372 / 0.419271 (-0.361899) | 0.032985 / 0.043533 (-0.010548) | 0.277717 / 0.255139 (0.022579) | 0.295692 / 0.283200 (0.012493) | 0.017756 / 0.141683 (-0.123927) | 1.166277 / 1.452155 (-0.285877) | 1.213337 / 1.492716 (-0.279380) |

### 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) | 0.091365 / 0.018006 (0.073359) | 0.296261 / 0.000490 (0.295772) | 0.000225 / 0.000200 (0.000025) | 0.000043 / 0.000054 (-0.000011) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.021973 / 0.037411 (-0.015438) | 0.074631 / 0.014526 (0.060106) | 0.085645 / 0.176557 (-0.090911) | 0.125181 / 0.737135 (-0.611955) | 0.086893 / 0.296338 (-0.209445) |

### 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) | 0.294110 / 0.215209 (0.078901) | 2.855531 / 2.077655 (0.777876) | 1.583204 / 1.504120 (0.079084) | 1.453911 / 1.541195 (-0.087284) | 1.467031 / 1.468490 (-0.001460) | 0.581214 / 4.584777 (-4.003562) | 2.423626 / 3.745712 (-1.322086) | 2.736665 / 5.269862 (-2.533197) | 1.707000 / 4.565676 (-2.858676) | 0.061171 / 0.424275 (-0.363104) | 0.004789 / 0.007607 (-0.002818) | 0.344546 / 0.226044 (0.118502) | 3.530955 / 2.268929 (1.262027) | 1.962532 / 55.444624 (-53.482092) | 1.670207 / 6.876477 (-5.206270) | 1.669041 / 2.142072 (-0.473031) | 0.642298 / 4.805227 (-4.162929) | 0.115503 / 6.500664 (-6.385161) | 0.040729 / 0.075469 (-0.034740) |

### 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) | 0.973101 / 1.841788 (-0.868687) | 11.823894 / 8.074308 (3.749586) | 10.664592 / 10.191392 (0.473200) | 0.139848 / 0.680424 (-0.540576) | 0.015728 / 0.534201 (-0.518473) | 0.289135 / 0.579283 (-0.290148) | 0.271325 / 0.434364 (-0.163039) | 0.332253 / 0.540337 (-0.208085) | 0.416982 / 1.386936 (-0.969954) |

</details>
</details>

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