Coding standards for PHP Stan Level 6 and CS

Fixed all the outstanding issue, but used the wrong issue number for my commit message. You can find the commit at https://git.drupalcode.org/project/drd_agent/-/commit/c7a0f10402175deed5...

Here are some comments:

• The modules job_scheduler and monitoring are also required for testing, as they contain some functions that are called optionally.
• The empty tests in src/Agent/Action/DomainsReceive.php are very special, because we include external PHP files and they may do certain things with those variables, something that PHPStan can not know. Added some comments in the code to explain that.
• The hacked class wasn't found because the use statement had a typo.
• The condition at https://git.drupalcode.org/project/drd_agent/-/commit/c7a0f10402175deed5... is also tricky, since we forward the $context as a reference indirectly to call_user_func_array and that may change the values. Set this to be ignored by PHPStan.
• Removed the MCrypt part here, but it still needs to remain in DRD since it also still monitors Drupal 7 sites. But the DRD Agent for Drupal 10 doesn't need that any longer.

Just found a couple more issues in \Drupal\drd_agent\Agent\Action\Base that haven't been reported by PHPStan and committed their fixes as well.

There is now one issue left at web/modules/contrib/drd_agent/src/Agent/Action/Base.php:331 where I have no idea yet, how we could resolve this.

Automatically closed - issue fixed for 2 weeks with no activity.