Add NaN handling in softmax pattern in SDPA fusion

[gramalingam]

Add NaN handling in softmax pattern in SDPA fusion

[codecov]

Codecov Report

❌ Patch coverage is 4.22535% with 68 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.94%. Comparing base (7227655) to head (61f2295).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
onnxscript/rewriter/ort_fusions/sdpa_test.py	0.00%	68 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2593      +/-   ##
==========================================
- Coverage   70.07%   69.94%   -0.13%     
==========================================
  Files         223      223              
  Lines       26266    26320      +54     
  Branches     2602     2602              
==========================================
+ Hits        18405    18410       +5     
- Misses       6950     7000      +50     
+ Partials      911      910       -1     

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