cleanup: Reduce stack frame sizes to below 4096 bytes.

[iphydf]

This is currently only detectable in tests, because the main code uses VLAs where stack frame size is unknown at compile time.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.75%. Comparing base (52a2c1a) to head (0f12f38).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2823      +/-   ##
==========================================
- Coverage   72.90%   72.75%   -0.15%     
==========================================
  Files         150      150              
  Lines       30706    30707       +1     
==========================================
- Hits        22385    22341      -44     
- Misses       8321     8366      +45     

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