Feature request: inspection of the surrogate model

[oersted]

This is a larger feature request, just wanted to express the potential value, I don't expect this to be implemented any time soon.

It would be very useful to have an API to access the internal surrogate model that Simple(x) is building, as well as some utilities to plot the value function over the problem space.

It would be valuable to gain an intuition of the impact of each input parameter, especially when doing low-dimensional optimization with hand-engineered features. Actually, Simple(x) could be useful just to efficiently map-out the shape of a search space for gaining a better understanding, besides blind black-box optimization.