Draft: Rewriting BeamFeedback as Subclasses
The LLRF beam feedback update presented in the BLonD meeting of 17.11.2023.
Some unittests and examples also had to be updated to conform to the new syntax for beam feedback classes. Additionally, the broken unittest for beam feedbacks has been fixed and a new one added.
Some ToDos are still left and in need of discussion, but the code for beam feedbacks should be equivalent to the one currently used.