Add PHP 8.4 support and require PHP 8.3+

[sylfabre]

Summary

• Update minimum PHP requirement to 8.3
• Add PHP 8.4 to CI test matrix

Changes

• Update composer.json to require PHP ^8.3
• Update GitHub Actions workflow to test on PHP 8.3 and 8.4

Related

Part of organization-wide upgrade to standardize on PHP 8.3+ across all packages.

Test plan

• CI tests pass on PHP 8.3
• CI tests pass on PHP 8.4

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud