Speed up computation of event_generation_hooks

[henrypinkard]

AcqEngJ:

event generation occurs on a separate thread from event execution. It should be possible to cache a small number of events in advance of execution so that any computations needed in generation arent limited by event execution speed

Thinking specifically of starting an acq with Magellan GUI, and wanting to insert SLM patterns using an acquisition hook, the patterns should be allowed to compute quickly regardless of the speed the events are executing at