Drupal 11 compatibility

Let's into it.

Thanks @manuel.adan. Everything seems to be working.
I tested it on a new D11 site with the "A practical use case" tutorial, everything works.

All right @pearls, thank you for your review. IEF compatibility was addressed by checking the signature of parent class. That way, we avoid to launch a new major version which is preferable, e.g. for easy upgrading sites using Transaction from D10 to D11.

Tests passed in D9 (PHP 8.1), D10 & D11 (PHP 8.4).