Error node needs optimization to reduce introduced circuitry

[rokopt]

The error node used by clients to throw a form of exception (see #90 and #129) currently introduces a lot of new circuitry through the addition of many Maybes. This will need optimization. @mariari has suggested introducing a crash type for cases where we don't need to pass errors back but can simply terminate the computation (ideally inducing VampIR to return some selected error code).