whisper : faster beam_search sampling via reduced KV cache copies (#1243)

whisper : faster beam_search sampling via reduced KV cache copies (#1243)

* Faster `beam_search` sampling

Refine the KV cache update logic for more intelligent and efficient updating.

* Faster `whisper_sample_token_topk`

* Update whisper.cpp

* Update whisper.cpp

* Update whisper.cpp

* Reduce `memory allocation`

* Add `pointer swapping`

* Fixed some bugs

* Update whisper.cpp

* Apply suggestions from code review

* Updated the logic for determining `two-copy`

* Updated the logic for determining `two-copy` v2

* whisper : add debug logs + coding style

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Co-authored-by: Georgi Gerganov <redacted>