Use a explicit state machine when running workflows

The current action engine runner uses an implicit state machine, this makes it difficult to read and understand. It would benefit from a explicit state machine with well defined transitions. This also is a good starting point to introduce a state machine type that can be used more extensively in taskflow (and elsewhere) as the concept/code gets flushed out (we have to start somewhere to get somewhere else, so this baby step seems like a good starting point, and one that is key to how taskflow runs workflows).