split module for CESK store

[kostmo]

Towards #1715 and #1043.

A follow-on to #1729; this refactoring step is a prerequisite for #1719 to extricate references to the CESK module from the base RobotR definition.

Motivation

Originally tried in #1731 to just remove dependence of TRobot on the RobotContext record, since RobotContext depends on Store which is defined in the CESK module However, this attempt did not work. So instead, we split the definition of Store out of the CESK module and allow TRobot to continue to depend on RobotContext.

[byorgey]

So is the idea that by splitting out this module we can keep Swarm.Game.CESK.Store in the scenario construction library with Robot, and Swarm.Game.CESK would go in the swarm-engine library? I don't like that, since, again, Store really has nothing to do with scenario construction and everything to do with the runtime system, and there's no reason a template robot should ever need to have a Store. In other words I'm not sure this is the correct place to do the split.

Looking at the definition of RobotContext, I think perhaps the Store really doesn't belong there. Everything else in the RobotContext stores information about defined names; notice the At instance, which returns the type, value, and requirements for a name (using the first three components of a RobotContext) but has nothing at all to do with the defStore. Although it would be more work, I think perhaps the correct way to do this is to split the defStore out of the RobotContext and store it in the Robot record separately, but using a type family so that it stores () in a TRobot and an actual Store in a concrete Robot. There is no reason a template robot should ever need to have a Store.

By the way, all this refactoring is annoying but I'm actually really happy with this process so far, and I really appreciate your work here. Splitting into sublibraries like this is really forcing us to think through some things that are too tightly coupled, and it's resulting in refactored code that is cleaner and more sensible.