Fix PHPStan issues

Hii,

It will be good to work on this after merging the MR of https://www.drupal.org/project/content_model_documentation/issues/3517038 📌 Fix PHP CS errors Active to avoid any conflicts. Let me know your view. Thanks!

Good idea. It is merged now so you should be clear.

Hii,

I have tried to resolve some of the errors. But there are still many errors that needs to be taken care.
Thanks!