chore: require PHP 8.4

[simPod]

Summary

• raise the library's minimum supported PHP version from 8.3 to 8.4 in composer.json
• move CI jobs and the lowest-dependency test leg to PHP 8.4 so the baseline matches the package requirement
• keep the broader CI matrix coverage on newer PHP versions unchanged

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.63%. Comparing base (ba53c13) to head (09bd11c).

Additional details and impacted files

@@           Coverage Diff           @@
##            0.2.x      #83   +/-   ##
=======================================
  Coverage   83.63%   83.63%           
=======================================
  Files           6        6           
  Lines          55       55           
=======================================
  Hits           46       46           
  Misses          9        9           

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