Move huggingface-hub dependency to optional test dependencies.

[crawftv]

References the issue I created #1845
#1845

I propose moving the huggingface_hub dependency to the optional testing dependencies to make installs easier and cleaner.

[Narsil]

That's not possible.

tokenizers HARD depends on huggingface_hub for the "from_pretrained" function.
It seems the issue you had was with hf-xet, and should be fixed soon. I'll close this PR for now, but let's reopen if there's anything that actually makes this http dependency problematic for other reasons. (I'll admit this dependency is only for a single function, which should be replaceable in 2 lines, but still it would be a huge breaking change to remove it since basically most HF code uses it.)