Hmm, I know we talked about this, but is there an advantage to having this in the `simulator` call as opposed to setting the seed on the model before calling `simulator`? I thought `Model.seed` would essentially set both the `model_seed` (which makes the build process deterministic) and `seed` (which makes simulation steps deterministic). But as it is here, `Model.seed` is just `model_seed` right? I think it's good to make it possible to have these two seeds separate, but I think the default should be that if you set `Model.seed` everything is deterministic. Then if you pass some kind of `sim_seed` to `Model.simulator`, the build process is the same, but the sim's RNG seed changes.