Remove graph breaks for torch.compile() in padding free branch in DataCollatorForCompletionOnlyLM

[Abhishek-TAMU]

What does this PR do?

This PR adds cu_seq_lens_q, cu_seq_lens_k, max_length_k, max_length_q to the batch in DataCollatorForCompletionOnlyLM. This, together with a PR in transformers (link to be added), removes graph breaks in padding-free tuning, allowing for maximum performance to be obtained.
Specifically, these parameters should be generated here (this PR change), outside of the transformers loop, as they incur a cpu-gpu sync that is unavoidable. Otherwise, this cpu-gpu sync happens here, inside the attention call which causes graph breaks and hence the transformers PR removes this call to remove all graph breaks when torch_compile flag is turned on in Training arguments to use in SFTTrainer.

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[Abhishek-TAMU]

CC: @kashif @qgallouedec

[HuggingFaceDocBuilderDev]

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[qgallouedec]

Hi, thanks for the PR.
Can you provide the link of the PR in transformers? Is it huggingface/transformers#33932?

[qgallouedec]

Could you provide a simple test to:

1. Confirm that it is a case of non-functioning.
2. Verify that this addition resolves it.

It might also be helpful to add a few comments, as these lines are unclear without context.