🪲 Allow Acts and Events to trigger at different times

The StartTrigger implementation did not store its success state and fell back to running in every consecutive step. This prevented children to execute and consequently, StartTrigger of children (e.g. act -> events) could never succeed at the same time. If a trigger now succeeds, its state is stored and children can check their trigger independently (not only at the very same timestep).

Closes #25 (closed)