Refactor dereference operations into tagged unions

[distributivgesetz]

It's just like rust enums no wayyyy

This PR tackles mainly nullability by refactoring the existing Dereference operation to be safer with the help of the type system.

The previous implementation used a struct called Operation, which held an enum value for what kind of operation the struct described as well as metadata about the operation. This resulted in a struct where pretty much every additional metadata was optional and had to be asserted at the time of checking Kind, which wasn't very elegant.

I refactored dereference operations by binding the metadata into types with one shared superclass called Operation.
The subclasses are there to describe all kinds of different metadata that they need. To get the metadata, you can use type patterns to extract the data. This completely eliminates the need to assert no nullability with !, making the code much clearer and more elegant.

Since Operation had to inherit from other things now, I had to turn it into a class. This has zero impact on performance since all operations were located on the heap anyways.

Additionally I cleaned up some of the code involving dereferences. One less area with warnings.