Verify validity of state root provided in block fraud proof

[Manav-Aggarwal]

When an optimint full node or light node receives a fraud proof, it needs a way to verify that the pre-state root provided in the fraud proof is actually existent on-chain as a first step in fraud proof verification which is what #581 does.

Now, we need to use this merkle root in the header.

Depends on: #581