Xet download workflow (#2875)
* first draft
* remove comment
* hf_xet instead of xet
* update docstring
* fix
* update docstring
* simplify typing
* quality
* add logging
* fix tests
* add unit tests for xet utilities
* first draft of download testing
* more tests
* address some comments
* fix tests
* check if hf_xet is available or not
* remove unnecessary dest dir creation
* keep comment
Co-authored-by: Lucain <lucain@huggingface.co>
* post-review improvements
* Update tests/test_xet_download.py
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Co-authored-by: Lucain <lucain@huggingface.co>
