feat(protocol): add preconf slasher

[AnshuJalan]

This PR covers Preconfirmation Structure, Preconfirmation Violations, Missing EOP and Invalid EOP sections of our LLD doc

[AnshuJalan]

I feel I will also be including Preconf EOP violations in this same contract. I was inclining toward having a separate contract for EOPs, but now that I think about it, the preconfer would then need to opt into another contract just for EOP. This is inconvenient.

[dantaik]

I know we briefly discussed this in our call, but I still prefer using an enum here. It allows us to explicitly mark a block as one of the following:

• 1: Start of a batch
• 2: End of a batch, but not end of preconfirmation
• 3: End of a batch and end of preconfirmation
• 0: All other blocks

By enforcing the correct marker for each block, it becomes easier to identify mistakes. Also, if we decide not to use markers 1 and 2, we don’t need to change the protocol at all. Using an enum gives us this flexibility.

[dantaik]

what if block X and block X+1 are in the same batch?

[AnshuJalan]

nextBatchMetadata stays empty in that case. I think the suggestion on keeping evidences separate will make this clearer.