[Refactor] Randao module

[Arkenan]

Both the representation of the randao list inside of a beacon state and its operations should be inside of a separate module. This allows two main things:

1. Have basic things like circular getters and setters in that module. We shouldn't need to calculate the remainder and adding the size of the list to avoid underflow everywhere in the code.
2. Representation can change to stuff like an Aja.vector for quicker replace operations if needed.