Proto: Adaptive slashing amount

Depends on !11773 (merged)

What

https://docs.google.com/document/d/1sxjJ_cpO-kgFFBpupxz7wu5-nEt2T73KpKRBlLEVHhg/edit#heading=h.vb9j318ygdzd

Why

How

We recompute the rights at the moment of the slash for the time that is slashed, then aggregate all the slots that have been slashed for the misbehaving block, and compute the correct slashing value. This involves some refactoring here and there, and building a temporary map indexed by misbehaviours

Manually testing the MR

Checklist

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