CI: update to clang-tidy 22, fixes, updates

[biojppm]

CI updates and fixes:

• Fix flaky single header test (targets were always amalgamating)
• Update clang-tidy to 22 (also fix warnings)
• Update github action versions
• Speed up embedded workflow

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.25%. Comparing base (de1bc78) to head (a6b181c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #624   +/-   ##
=======================================
  Coverage   99.25%   99.25%           
=======================================
  Files          49       49           
  Lines       13921    13921           
=======================================
  Hits        13817    13817           
  Misses        104      104           

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