The state of each PRNG in `ctx.component['random']` is now saved to, and
restored from, the cache file.

Summary tables can now save and restore their internal state, similar to
summary monitors, and the SimulatedObs table now caches the state of the
PRNGs that it uses for resampling particles and simulating observations.
This means that the contents of tests/simulated_obs.ssv have changed.