CI: moderinize compilers and cleanup

[wirew0rm]

• add gcc13 and clang17
• remove clang15
• also run on PRs not targeted at main
• emscripten: change from difficult to maintain hash (was a workaround to use the system nodejs) to proper releases
• emscripten: update version from 3.1.30 to 3.1.43

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (df17c90) 55.83% compared to head (97f6ac1) 56.17%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #319      +/-   ##
==========================================
+ Coverage   55.83%   56.17%   +0.34%     
==========================================
  Files          65       65              
  Lines        7202     7083     -119     
  Branches     2626     2622       -4     
==========================================
- Hits         4021     3979      -42     
+ Misses       1510     1433      -77     
  Partials     1671     1671              

see 31 files with indirect coverage changes

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