SCORU: Do not rehash to convert hashes, use of_bytes/to_bytes

@lthms told me that one can convert one hash h of module H1 into a hash of module H2 by doing H2.of_bytes (H1.to_bytes h) instead of doing H2.hash_bytes [H1.to_bytes h].

Please, confirm and apply this to all hashes conversion we are doing, e.g., context_hash_to_state_hash.