Add GQA test for sdpa_with_kv_cache large seq length (#4324)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4324

Plus some refactor. More refactor can be done later
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ghstack-source-id: 234820964
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Reviewed By: manuelcandales

Differential Revision: D60045236

fbshipit-source-id: ac9f4a95b7735b63828ff93a18a2a3e87df4b8e9