feat(SlevomatCodingStandard.Functions.StaticClosure): enable again

[pekral]

Additional notes

Znovu povolit v code base SlevomatCodingStandard.Functions.StaticClosure mimo testy, protože PEST nechce static closures.

[pekral]

Implementation complete

The fix is implemented in PR #57.

What to test

1. Add a non-static closure to production PHP code (e.g. $fn = function() { return 1; };) — PHPCS should now flag it and require static keyword.
2. Add a non-static closure inside a test file under tests/* — PHPCS should not flag it (PEST compatibility).
3. Run composer check to verify no violations in production code that uses static closures correctly.