Re-verify failed blocks if finalized

[samliok]

We have a one-time verifier that saves the result of block verification. However, it's possible that a block has not verified for our node but got accepted & finalized by a quorum of nodes in the network. This can happen since block proposers include timestamps which can be up to a threshold greater than our node's current timestamp. Therefore, our node can see a block that it thinks is too far ahead while others think the block is acceptable due to clock synchrony issues.

[yacovm]

That's a good point, however a bigger problem is not the clock synchrony but rather the advancement of the P-chain.