Skip default stateRoot and codeHash in accounts

[s1na]

In turbo-token we'll only need nonce and balance. To keep "compatibility" with eth1 (e.g. same state root hashes), we nevertheless consider the account to have a stateRoot and a codeHash. But since they're usually default values, they can be set to 0 or come with a flag, to reduce block data.

[s1na]

This would reduce data size, but come at the cost of speed. The EE would have to add the default values for stateRoot and codeHash to the account and re-encode to be able to verify the proof.