Relax stage checking for getObjVal, getVal

[Joao-Dionisio]

getObjVal, getVal are too strict in the stage checks. For example, the following code crashes:

from pyscipopt import Model

m = Model()

x = m.addVar()
m.setObjective(x)

m.setParam("limits/solutions", 1)
m.optimize()

print("Stage: ", m.getStage())

print(m.getNSols())
print(m.getObjVal()) # crashes here, even though the model does have solutions

I changed it to reflect SCIP.

I also removed the noexcept from the code, because I couldn't compile otherwise. It's probably me being a dummy, but I do have Cython >= 3 (EDIT: It was me being a dummy). Of course, I imagine that not removing them is desirable.

EDIT2:

Okay, right now I'm having segfaults in test_customizedbenders.py, and I'm pretty sure it's because self._bestSol.sol is NULL, but I can't figure out why that is.

[Joao-Dionisio]

PR closed while there are still problems with it. Opened issue #847 to keep track of it.