More efficient set representations

[schillic]

(This is a long-term nice-to-have thing.)

Instead of an intersection of HalfSpaces we can often create more efficient set representations, like Hyperrectangles.

In particular, since we add the affine term via a CartesianProduct with a Singleton([1]) to each set in U, one should detect this pattern and simplify (S * H1) ∩ (S * H2) = S * (H1 ∩ H2) = S * Box.