transformations: stencil-bufferize side-effect analysis fix

[PapyChacal]

Just forgot to check side-effects including the last user when fold stencil.buffer

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.90%. Comparing base (bd700e9) to head (c869531).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3076   +/-   ##
=======================================
  Coverage   89.90%   89.90%           
=======================================
  Files         418      418           
  Lines       52898    52902    +4     
  Branches     8200     8202    +2     
=======================================
+ Hits        47556    47560    +4     
  Misses       4015     4015           
  Partials     1327     1327           

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