Fix filelock if flock not supported

[Wauplin]

Fix #2399 (cc @jeffliu-LL)

On unix, filelock checks if fcntl is available. If it is, filelock.Filelock is in fact a UnixFileLock which uses fcntl.flock to acquire/release the lock. Since it's a system call, the lock is supposed to be much more robust (e.g. does not rely on file existence or not). The problem is that if fcntl is available but at least one partition or filesystem does not support it, a NotImplementedError exception is raised with message "FileSystem does not appear to support flock; use SoftFileLock instead".

This PR fixes usage of filelok by catching this NotImplementedError when it happens and defaulting back to a SoftFileLock. This is a weaker solution but for our use case it should be fine (+ it's already the filelock used by default on win32).

[HuggingFaceDocBuilderDev]

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[LysandreJik]

Ok! I learned a few things reading the description, thanks for making it so clear!

[Wauplin]

I've learnt a few things myself and will probably have forgotten them next time I need to come back to this PR! Hope the PR description will save us then 😄