Introduce PHPStan and adjust minimum requirements

[lloc]

This PR introduces PHPStan with the initial level set to 1, with the goal of gradually increasing it to at least 5 or higher over time.

Changes and Improvements

• PHPStan Integration

  • PHPStan can be executed locally using composer phpstan.
  • It has also been added as an additional GitHub workflow for automated checks.

• Minimum PHP and WordPress Requirements

  • PHPStan requires at least PHP 7.2, so this PR suggests:
    • Dropping support for PHP 5.6.
    • Setting the minimum requirements to WordPress 5.1 and PHP 7.2.
  • As a sidenote, WordPress 5.1 includes a fix for a bug in the test suite introduced after version 4.x.

• PHP 8.4 Compatibility

  • PHP 8.4 has been added to the test checks.

[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