Migrate multipack to refactored flash attention

[casper-hansen]

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🔖 Feature description

Transformers recently refactored flash attention. At current point in time, axolotl replaces the _get_unpad_data for its multipack feature. Instead, replace the central _get_unpad_data in the new transformers. https://github.com/huggingface/transformers/pull/31446

✔️ Solution

Replace the long if-statement in monkeypatch/multipack and directly replace the centralized unpad function:

        transformers.modeling_flash_attention_utils._get_unpad_data = (  # pylint: disable=protected-access
            get_unpad_data
        )

❓ Alternatives

No response

📝 Additional Context

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Acknowledgements

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[winglian]

this should be fixed with #1773 , I just need to do some manual testing