fix: use composer exec instead of castor to run PHPUnit and avoid .castor.stub.php generation

Replace 'castor phpunit' with direct 'composer exec -- phpunit-11' to prevent the auto-generation
of .castor.stub.php file which causes interface redeclaration errors in PHP 8.2-8.3:
'Cannot declare interface Psr\Cache\CacheItemInterface, because the name is already in use'

When Castor runs, it automatically generates .castor.stub.php for IDE support, which contains
stub definitions that conflict with real PSR interfaces from Composer dependencies.

By using composer exec directly, we avoid running Castor altogether and prevent the stub file
from being generated during test execution.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: Spomky

.github/workflows/ci.yml

@@ -206,7 +206,7 @@ jobs:
           fi
 
       - name: Run PHPUnit
-        run: castor phpunit
+        run: composer exec -- phpunit-11 --coverage-xml .ci-tools/coverage --log-junit=.ci-tools/coverage/junit.xml --configuration .ci-tools/phpunit.xml.dist --display-warnings --display-deprecations
 
   infection:
     name: "🧬 Mutation Testing"