Bump grpcio-tools to 1.81.1 for Python 3.14 build

[aIbrahiim]

Test plan

• Confirm Windows Python 3.14 unit tests / wordcount install grpcio-tools from wheel (no source build / D8016)
• Confirm Build python cp314- wheels on auto for windows-latest succeeds
• Spot-check Python 3.13 / <=3.12 builds still use their existing pins

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.81%. Comparing base (eab1bce) to head (5891306).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #39714   +/-   ##
=========================================
  Coverage     58.80%   58.81%           
  Complexity     7638     7638           
=========================================
  Files          1663     1663           
  Lines        216332   216368   +36     
  Branches       6536     6536           
=========================================
+ Hits         127219   127259   +40     
+ Misses        84401    84397    -4     
  Partials       4712     4712           

Flag	Coverage Δ
python	79.88% <ø> (+0.01%)	⬆️

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