Start a new consensus round if we get stuck

[hewison-chris]

For example as suggested here if a pending block takes too long to get a majority of signatures:

Next step IMO is to put a timeout on how long a pending block can exist and if we reach it, start a new consensus round. so our assumption `block_height == slot_idx` won't hold anymore.

_Originally posted by @omerfirmak in https://github.com/bosagora/agora/issues/3039#issuecomment-1046482920_

But perhaps this could also be used once we get behind block schedule and are not making progress during nomination phases.