fix `DatasetBuilder._split_generators` incomplete type annotation

solve  #6798:

add missing `StreamingDownloadManager` type annotation to the `dl_manager` argument of the `DatasetBuilder._split_generators` function

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6799). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

The CI failures are unrelated to the changes

<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) | 0.004974 / 0.011353 (-0.006378) | 0.003153 / 0.011008 (-0.007856) | 0.062785 / 0.038508 (0.024277) | 0.029504 / 0.023109 (0.006395) | 0.245558 / 0.275898 (-0.030340) | 0.274022 / 0.323480 (-0.049457) | 0.003173 / 0.007986 (-0.004813) | 0.002643 / 0.004328 (-0.001686) | 0.048917 / 0.004250 (0.044667) | 0.042965 / 0.037052 (0.005912) | 0.261266 / 0.258489 (0.002777) | 0.291546 / 0.293841 (-0.002295) | 0.027860 / 0.128546 (-0.100686) | 0.010397 / 0.075646 (-0.065249) | 0.205981 / 0.419271 (-0.213290) | 0.035663 / 0.043533 (-0.007870) | 0.250466 / 0.255139 (-0.004673) | 0.273947 / 0.283200 (-0.009253) | 0.016659 / 0.141683 (-0.125023) | 1.147884 / 1.452155 (-0.304270) | 1.187609 / 1.492716 (-0.305107) |

### 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) | 0.095564 / 0.018006 (0.077558) | 0.300086 / 0.000490 (0.299597) | 0.000212 / 0.000200 (0.000012) | 0.000049 / 0.000054 (-0.000005) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.018100 / 0.037411 (-0.019311) | 0.061342 / 0.014526 (0.046816) | 0.073747 / 0.176557 (-0.102810) | 0.120577 / 0.737135 (-0.616559) | 0.075797 / 0.296338 (-0.220541) |

### 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) | 0.288766 / 0.215209 (0.073557) | 2.835274 / 2.077655 (0.757620) | 1.515288 / 1.504120 (0.011168) | 1.396097 / 1.541195 (-0.145098) | 1.424293 / 1.468490 (-0.044197) | 0.568356 / 4.584777 (-4.016421) | 2.393171 / 3.745712 (-1.352541) | 2.756219 / 5.269862 (-2.513642) | 1.731343 / 4.565676 (-2.834334) | 0.062542 / 0.424275 (-0.361733) | 0.005385 / 0.007607 (-0.002223) | 0.340876 / 0.226044 (0.114832) | 3.376649 / 2.268929 (1.107720) | 1.856135 / 55.444624 (-53.588490) | 1.581802 / 6.876477 (-5.294675) | 1.591081 / 2.142072 (-0.550992) | 0.647963 / 4.805227 (-4.157264) | 0.119218 / 6.500664 (-6.381446) | 0.042660 / 0.075469 (-0.032809) |

### 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) | 1.005017 / 1.841788 (-0.836770) | 11.670779 / 8.074308 (3.596471) | 9.533790 / 10.191392 (-0.657602) | 0.141571 / 0.680424 (-0.538853) | 0.013987 / 0.534201 (-0.520214) | 0.286598 / 0.579283 (-0.292685) | 0.260123 / 0.434364 (-0.174240) | 0.324186 / 0.540337 (-0.216151) | 0.421246 / 1.386936 (-0.965690) |

</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) | 0.005196 / 0.011353 (-0.006157) | 0.003697 / 0.011008 (-0.007311) | 0.049530 / 0.038508 (0.011022) | 0.030892 / 0.023109 (0.007783) | 0.284787 / 0.275898 (0.008889) | 0.302833 / 0.323480 (-0.020647) | 0.004203 / 0.007986 (-0.003783) | 0.002736 / 0.004328 (-0.001592) | 0.050203 / 0.004250 (0.045953) | 0.040335 / 0.037052 (0.003283) | 0.292508 / 0.258489 (0.034019) | 0.317918 / 0.293841 (0.024077) | 0.029144 / 0.128546 (-0.099403) | 0.010171 / 0.075646 (-0.065475) | 0.058130 / 0.419271 (-0.361141) | 0.032743 / 0.043533 (-0.010790) | 0.281354 / 0.255139 (0.026215) | 0.296951 / 0.283200 (0.013751) | 0.018399 / 0.141683 (-0.123284) | 1.158852 / 1.452155 (-0.293303) | 1.189750 / 1.492716 (-0.302966) |

### 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) | 0.093073 / 0.018006 (0.075066) | 0.301779 / 0.000490 (0.301290) | 0.000209 / 0.000200 (0.000009) | 0.000051 / 0.000054 (-0.000003) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.021565 / 0.037411 (-0.015846) | 0.075237 / 0.014526 (0.060711) | 0.087368 / 0.176557 (-0.089188) | 0.126955 / 0.737135 (-0.610180) | 0.088456 / 0.296338 (-0.207883) |

### 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) | 0.291225 / 0.215209 (0.076016) | 2.863220 / 2.077655 (0.785565) | 1.616936 / 1.504120 (0.112817) | 1.500553 / 1.541195 (-0.040641) | 1.501693 / 1.468490 (0.033203) | 0.560118 / 4.584777 (-4.024659) | 2.439241 / 3.745712 (-1.306472) | 2.786804 / 5.269862 (-2.483058) | 1.737772 / 4.565676 (-2.827905) | 0.063668 / 0.424275 (-0.360607) | 0.005320 / 0.007607 (-0.002287) | 0.344539 / 0.226044 (0.118495) | 3.418803 / 2.268929 (1.149874) | 1.981791 / 55.444624 (-53.462834) | 1.698484 / 6.876477 (-5.177993) | 1.686815 / 2.142072 (-0.455258) | 0.646911 / 4.805227 (-4.158316) | 0.116969 / 6.500664 (-6.383696) | 0.040380 / 0.075469 (-0.035089) |

### 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) | 1.017337 / 1.841788 (-0.824451) | 11.858212 / 8.074308 (3.783904) | 10.270287 / 10.191392 (0.078895) | 0.154266 / 0.680424 (-0.526158) | 0.014886 / 0.534201 (-0.519315) | 0.292354 / 0.579283 (-0.286929) | 0.270888 / 0.434364 (-0.163476) | 0.333289 / 0.540337 (-0.207049) | 0.423001 / 1.386936 (-0.963935) |

</details>
</details>

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