Returns the next app tag for a given sender and recipient pair.
Returns the next sender-side index for a constrained-delivery shared secret.
Notifies the simulator that a note has been created, so that it can be returned in future read requests in the same
transaction. This note should only be added to the non-volatile database if found in an actual block.
Notifies the simulator that a note has been nullified, so that it is no longer returned in future read requests in
the same transaction. This note should only be removed to the non-volatile database if its nullifier is found in an
actual block.