integration with rewrite programming

Some processes may require complicated sequences of events to take place, which could in principle be orchestrated with a ton of timers and dirac deltas and injection of implementation details into the world state ... but perhaps should be explicitly expressed as programs of a sort. Rather than Julia programs, though, we can use the graphical languages for schedules in [AlgebraicRewriting](https://www.krisb.org/docs/slides/abm_demo_2023/). An example where this may be especially important is having support for declaring model initialization procedures.

One means this could be integrated is generalizing `ABMRule` to take a stochastic timer and a whole _schedule_, of which the schedule which contains just a single rewrite rule is a special case.