Refactor castor validation and integrate tasks in workflows

The code refactors the validation of the composer configuration and autoload dumping in the 'castor.php' file. It also modifies the '.github/workflows/integrate.yml' to replace previous tasks with equivalent 'castor' commands for validation, testing, static analysis, code style checking, Deptrac analysis, and make rector. Additionally, '.castor.stub.php' is added to the '.gitignore' file to prevent it from being tracked.