More webdataset fixes
...by pinning a more recent version of `datasets@datasets-2.19.1-hotfix`

The webdataset fixes are needed for a dataset release, see [internal](https://huggingface.slack.com/archives/C06T0REVAH1/p1716998706658099?thread_ts=1714048738.307959&cid=C06T0REVAH1)

<s>I also included your fix for the columns order and Json improvement @albertvillanova </s>
More webdataset fixes: ...by pinning a more recent version of `datasets@datasets-2.19.1-hotfix`

The webdataset fixes are needed for a dataset release, see [internal](https://huggingface.slack.com/archives/C06T0REVAH1/p1716998706658099?thread_ts=1714048738.307959&cid=C06T0REVAH1)

<s>I also included your fix for the columns order and Json improvement @albertvillanova </s>