[signer] event parity should apply to all incoming signer messages

[jferrant]

Currently event parity is only applied to a block proposal. It should be applied to both SignerEvent::BlockValidationResponse(_) and Some(SignerEvent::MinerMessages(..)). The lack of proper reward cycle checks caused the chain to stall. See #5612

This will require changes to both the node and the signer.

As part of this ticket, remove the parity check within the hotfix handle_block_validate_* fns as it should be done in the outer call (also prevents double incrementing metrics when they shouldn't be)