Bump minimum PHP version to 8.4

[simPod]

Summary

• Bump minimum PHP version from 8.3 to 8.4 in composer.json
• Update all CI workflow matrices to use PHP 8.4 as the minimum version

Test plan

• CI passes with PHP 8.4
• Verify no PHP 8.3-only syntax or features are relied upon

https://claude.ai/code/session_01PUrXPtpExW4NVGDWx2zCFY

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.49%. Comparing base (c0580d3) to head (201178c).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #318   +/-   ##
=======================================
  Coverage   94.49%   94.49%           
=======================================
  Files          42       42           
  Lines         709      709           
=======================================
  Hits          670      670           
  Misses         39       39           

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