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* refactor how attention kernels from hub are used.

* up

* refactor according to Dhruv's ideas.
Co-authored-by: Dhruv Nair <dhruv@huggingface.co>

* empty
Co-authored-by: Dhruv Nair <dhruv@huggingface.co>

* empty
Co-authored-by: Dhruv Nair <dhruv@huggingface.co>

* empty
Co-authored-by: dn6 <dhruv@huggingface.co>

* up

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Co-authored-by: Dhruv Nair <dhruv@huggingface.co>
Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>

* add aiter attention backend

* Apply style fixes

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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

* add a lightweight test suite for attention backends.

* up

* up

* Apply suggestions from code review

* formatting