Added tests for bundle classes

[stixx]

This PR establishes the testing foundation and CI pipeline for the bundle.

Changes:

• Test Suite: Added 134 unit and functional tests covering routing, validation, and response handling.
• CI Pipeline: Configured GitHub Actions for automated testing, linting (PSR-12), and static analysis.
• Static Analysis: Resolved all type-related issues to achieve a clean PHPStan run at level max.
• Stabilization: Fixed several cross-platform casing issues and refined OpenAPI attribute scanning.

Verification:

• PHPUnit: 134 tests passed.
• PHPStan: Level Max achieved.
• Code Style: Verified via php-cs-fixer.