Implement Counter-example or Solution Cache

[feliam]

The counter-example cache maps sets of constraints to a variable assignments that solves it, or flag it as no sat. By storing the cache in this fashion, the solutions cache gains three additional ways to eliminate queries.

1- When a subset of a constraint set has no solution, then neither does the original constraint set. Adding constraints to an unsatisfiable constraint set cannot make it satisfiable.

2- When a superset of a constraint set has a solution, that solution also satisfies the original constraint set. Dropping constraints from a constraint set does not invalidate a solution to that set.

3- When a subset of a constraint set has a solution, it is likely that this is also a solution for the original set. Checking a potential solution is cheap.

Research, implement and add tests for it.
Defining a new CounterExampleConstraintSet class may be the way to go.