fun notifyAll(txns: Iterable<WireTransaction>): Vault
Possibly update the vault by marking as spent states that these transactions consume, and adding any relevant new states that they create. You should only insert transactions that have been successfully verified here
Returns the new vault that resulted from applying the transactions (note: it may quickly become out of date).
TODO: Consider if theres a good way to enforce the must-be-verified requirement in the type system.