Improve GQA fusion

[justinchuby]

Output present key value from the Attention op because past key value is provided.

Replaces #2632

[Copilot]

Pull Request Overview

This PR improves GQA (Grouped Query Attention) fusion by modifying the attention operation to output present key-value pairs in addition to the attention result. The change ensures that both past and present key-value states are properly handled in the fused operation.

• Modified the pattern function to return present key and value tensors alongside the attention output
• Updated the rewrite function to specify 3 outputs for the attention operation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.38%. Comparing base (811937c) to head (3fb7223).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2634   +/-   ##
=======================================
  Coverage   70.38%   70.38%           
=======================================
  Files         222      222           
  Lines       26288    26288           
  Branches     2629     2629           
=======================================
  Hits        18503    18503           
  Misses       6865     6865           
  Partials      920      920           

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