Drop PHP 8.3 support, add PHP 8.5 to CI matrix

[simPod]

• Update composer.json minimum PHP requirement from ^8.3 to ^8.4
• Update CI coding-standard and phpstan jobs to use PHP 8.4
• Update PHPUnit matrix: test PHP 8.4 and 8.5 (was 8.3 and 8.4)
• Run lowest-dependency tests on PHP 8.4 instead of 8.3

https://claude.ai/code/session_01MUjCvaa5dkrD6v9nV6DkLy

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.90%. Comparing base (23ef89f) to head (c059431).
⚠️ Report is 1 commits behind head on 7.0.x.

Additional details and impacted files

@@           Coverage Diff           @@
##            7.0.x     #176   +/-   ##
=======================================
  Coverage   94.90%   94.90%           
=======================================
  Files           3        3           
  Lines         255      255           
=======================================
  Hits          242      242           
  Misses         13       13           

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