[HfFileSystem] improve cache for multiprocessing fork and multithreading (#3500)
* improve hffs cache for multiprocessing fork
* minor
* mypy
* fix for token
* add test
* fix for threading too
* comment
* fix CI: make HfHubHTTPError picklable
* fix tests
* better naming
* clear instance cache before testing to ignore remaning Mock objects
* don't test "fork" on windows
* Apply suggestions from code review
Co-authored-by: Lucain <lucain@huggingface.co>
* use insecure_hashlib
* style
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Co-authored-by: Lucain <lucain@huggingface.co>