fix(phpstan): resolve method and class checks

Several changes have been made, primarily around checking the existence of methods and classes and
removing unnecessary comments.

- Method checks have been introduced to ensure the `getCachePath()` method exists before calling it.
- Removed invalid phpDocs, e.g., @var $Site Site and @var $Project Project
- Fixed typing to align return types and updated a factory method to check class existence.
- Added variable definition comments in the settings.css.php file for clarity.

Related: #114