Fix xisfile, xgetsize, xisdir, xlistdir in private repo
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_The documentation is not available anymore as the PR was closed or merged._ Added tests for xisfile, xgetsize, xlistdir and xglob for private repos, and also tests for xwalk that was untested
`xisfile` is working in a private repository when passing a chained URL to a file inside an archive, e.g. `zip://a.txt::https://huggingface/datasets/username/dataset_name/resolve/main/data.zip`. However it's not working when passing a simple file `https://huggingface/datasets/username/dataset_name/resolve/main/data.zip`.

This is because the authentication headers are not passed correctly in this case.

This is causing dataset streaming to fail in private parquet repositories, as noted in https://github.com/huggingface/datasets/issues/4605

I fixed `xisfile` and the other functions that behave the same way: xgetsize, xisdir and xlistdir

TODO:
- [x] tests

fix https://github.com/huggingface/datasets/issues/4605
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