refactor: update to PHP 8.1 and PHPUnit 10.5 || 11.0

[paulbalandan]

Description Updates minimum PHP version to ^8.1 to align with CodeIgniter v4.5.0 and also updates PHPUnit to 10.5 || 11.0

Checklist:

• [x] Securely signed commits
• [x] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [x] Conforms to style guide