Manually triggered decisions should use schedule when setting deadlines

[jschwartzentruber]

If we cycle a fuzzing pool by manually triggering its hook, we set the new task deadlines based on the fuzzing config without regard for when the hook will next run based on the schedule. Since fuzzing-decision cancels existing tasks in the worker pool, this produces canceled tasks in Taskmanager which lack artifacts.

fuzzing-decision should check when the next scheduled hook will fire, and set deadlines accordingly. We'll still have some canceled tasks caused by manually cycling the pool, which can't be helped.