[Core] Enable hf_transfer by default if available

[michaelfeil]

This is a "quality of life" PR. It auto enables the hf_transfer backend of huggingface_hub. As explained in #2907, hf_transfer should be safe to use, e.g. is the default in TGI since pretty long. https://github.com/huggingface/text-generation-inference/blob/92bb56b0c1038a35f73a6c96c506f6d1c3d7b043/Dockerfile#L151
Enabling it with a env variable misses a fair amount of users + leads to hf_transfer beeing forced to be enabled globally - even if available just in this Python env.

Closes #2907 (fix)
Related #3031 #3008

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[njhill]

Thanks @michaelfeil this looks great. I'm wondering though should we check for whether the HF_HUB_ENABLE_HF_TRANSFER env var is set explicitly and only auto-enable if it isn't? To allow users to disable it if they need to when using the docker image for example.

[michaelfeil]

Thanks @michaelfeil this looks great. I'm wondering though should we check for whether the HF_HUB_ENABLE_HF_TRANSFER env var is set explicitly and only auto-enable if it isn't? To allow users to disable it if they need to when using the docker image for example.

Will follow up with: if HF_HUB_ENABLE_HF_TRANSFER is set, ignore any logic in vllm.

[njhill]

Thanks @michaelfeil!