Expire CVXOPT Dependency

[coreyostrove]

This finishes the expiration of the dependency on CVXOPT that we announced in the release of 0.9.13. The cvxpy dependency has had an associated minimum version requirement added.

See #437 for more.

[rileyjmurray]

Let's do the following instead

    objective_val = -2
    varvals = [_np.zeros_like(J), None, None]
    sdp_solvers = ['MOSEK', 'CLARABEL', 'CVXOPT']
    for i, solver in enumerate(sdp_solvers):
        try:
            prob.solve(solver=solver)
            objective_val = prob.value
            varvals = [v.value for v in vars]
            break
        except (AssertionError, _sdps.cp.SolverError) as e:
            msg = f"Received error {e} when trying to use solver={solver}."
            if i + 1 == len(sdp_solvers):
                failure_msg = "Out of solvers. Returning -2 for diamonddist."
            else:
                failure_msg = f"Trying {sdp_solvers[i+1]} next."
            msg += f'\n{failure_msg}'
            _warnings.warn(msg)

[rileyjmurray]

(I left almost the same comment verbatim in some other GitHub interface. I'm not sure where that comment went.)

[coreyostrove]

What is the import for _sdps?

[rileyjmurray]

Oh, whoops. It's on a branch where I made an sdptools.py file. All that matters is that _sdps.cp.SolverError is cvxpy.SolverError. So it'll suffice to import cvxpy as cp and then replace with cp.SolverError.

[coreyostrove]

Ok, I made this change with a small modification to skip producing warnings is MOSEK isn't installed, since we can assume this is pretty much always going to be the case for most users. (Read: I don't have MOSEK and didn't want to get constant warnings about that...)

While going through I also noticed that there was a flag disabling the diamond distance unit test on windows that was added about 3 years ago. The commit message on that indicated it was due to random CVXOPT failures on the runners. I'm going to blindly assume that the changes we're making plus the intervening three years probably fixed things on their own so reenabled those.