feat: trainer resume_from_checkpoint support hub downloads (#43375)

[aarushisingh04]

what does this PR do?

this pr enables trainer.train(resume_from_checkpoint=...) to accept hugging face hub repository ids.

instead of only local paths, users can now pass user/repo@revision and the trainer will automatically download the checkpoint using snapshot_download and resume training from it. this is particularly useful for preemptible cloud training where checkpoints are automatically pushed to the hub.

fixes #43375

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who can review?

@SunMarc