proof: verify keys, pre-state and post-state

[jsign]

This PR improves the proof verification code in many ways:

• We now check that the claimed keys in the proof actually match what we computed during the EVM block execution using the access witness.
• Same with the pre-state values, which we weren't checking.
• The post-state values validation now doesn't require building the post-state tree. What we do is use trie.VerkleTrie APIs to collect all tree-writes while StateDB dumps the dirty objects into the tree to calculate the new root. We then use these tree writes to figure which are the correct post-state values.

More about each point in comments.

TODO:

• [x] Extra test doing a proof gen+verif replaying of existing Kaustinen from genesis.