[Request] good_lp solver integration

[lmmx]

I'd like to be able to use Pumpkin as a solver backend from a Rust constraint programming framework, I know MiniZinc is available in Python but it'd be useful to have support in a Rust framework, and the library is already in Rust. I tried to add Pumpkin solver to the good_lp framework but I'm new to using it so while it's plumbed in OK the tests aren't passing. I suspect someone more familiar with it might be able to get it to work much more easily, if you've an interest in trying please find my attempt here

I suspect only a subset of the Pumpkin constraint types would be supported but in my view that's still worthwhile. I opened an issue over on good_lp in an attempt to gauge if this intuition is right:

• [Solver Proposal] Pumpkin support rust-or/good_lp#95
• feat: Add pumpkin_solver solver rust-or/good_lp#96