Fix CI and update Transformers (4.51.1)

[IlyasMoutawwakil]

What does this PR do?

Fixes the many CI issues by:

• Relaying all/most hub related communication to transformers methods (cached_file) since they're more maintained and can handle CI loads (TRANSFORMERS_IS_CI=true)
• Needed to update transformers to get @echarlaix's argmax fix in Fix ONNX export for sequence classification head  transformers#36332.
• Needed latest transformers 4.51.1 to get a fix that was part of the patch (weight initialization).
• used a really small whisper model (cuts onnxruntime testing ci by 40%)
• Mock torch_pre_mlir to pass MPT remote code tests.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.