Fix https://github.com/huggingface/datasets/issues/6750#issuecomment-2016678729

I didn't find a guideline on how to run the tests, so i just run the following steps to make sure that this bug is fixed.
1. `python test.py`,
2. then `HF_DATASETS_OFFLINE=1 python test.py`

The `test.py` is
```
  import datasets

  datasets.utils.logging.set_verbosity_info()

  ds = datasets.load_dataset('izhx/STS17-debug')
  print(ds)

  ds = datasets.load_dataset('C-MTEB/AFQMC', revision='b44c3b011063adb25877c13823db83bb193913c4')
  print(ds)
```



Fix cache path to snakecase for `CachedDatasetModuleFactory` and `Cache`
@lhoestq hi 😃, is there something else I need to do to check this change? I added two tests and passed them on my server.

```
pytest tests/packaged_modules/test_cache.py 
========================================================================== test session starts ==========================================================================
platform linux -- Python 3.11.5, pytest-8.1.1, pluggy-1.4.0
rootdir: /mnt/nas/datasets
configfile: pyproject.toml
plugins: xdist-3.5.0, datadir-1.5.0
collected 8 items                                                                                                                                                       

tests/packaged_modules/test_cache.py ........                                                                                                                     [100%]

========================================================================== 8 passed in 50.71s ===========================================================================

```

```
pytest tests/test_load.py
========================================================================== test session starts ==========================================================================
platform linux -- Python 3.11.5, pytest-8.1.1, pluggy-1.4.0
rootdir: /mnt/nas/datasets
configfile: pyproject.toml
plugins: xdist-3.5.0, datadir-1.5.0
collected 151 items                                                                                                                                                     

tests/test_load.py .............................................................................................................................................. [ 94%]
.........                                                                                                                                                         [100%]

...

============================================================= 151 passed, 29 warnings in 578.36s (0:09:38) ==============================================================
```
 The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_6754). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. Hi @izhx! I have also faced this issue, happy to see it already addressed, looking forward for PR merge :)