Improve scikit-learn compatibility for CleanTransformer + tests

[CarloLepelaars]

First of all, thank you for building and open-sourcing this! It has been very helpful for us at @crowdcent.

We ran into some issues when trying to use CleanTransformer as a component. These are:

1. fit should have y=None defined for compatbility so supervised training can be done where CleanTransformer is a component in a Pipeline.
2. It is standard since scikit-learn==1.1 to define get_feature_names_out (Source).

I've implemented these and wrote some accompanying tests. Would be happy to discuss any changes.