[consensus] Temporarily Stop Processing Signatures from Invalid Peers

[patrick-ogrady]

If we process a message from a peer that is invalid (missing fields, invalid signatures, etc.), we should temporarily stop processing messages from them to avoid wasted work.

We need to be careful here because a bug could lead to everyone dropping messages from each other (causing a consensus halt). We would want to potentially "limit" how many peers we're dropping from or just accept this as a possible outcome.