Derives the on-chain mailbox id for a msg key.
mailbox_id = SHA-256("raven/mailbox/v1/id" ‖ msg_key)
32-byte msg key from deriveMsgKey
32-byte mailbox id (the box name)
InvalidMsgKeyError if the key is not 32 bytes
Derives the on-chain mailbox id for a msg key.
mailbox_id = SHA-256("raven/mailbox/v1/id" ‖ msg_key)