Switch diamond distance solver

Switches to using Clarabel as the solver for diamond distance and adds a minimum version pin for cvxpy.

Author: Corey Ostrove

pygsti/tools/optools.py

@@ -323,7 +323,7 @@ def diamonddist(a, b, mx_basis='pp', return_x=False):
     prob, vars = _diamond_norm_model(dim, smallDim, J)
 
     try:
-        prob.solve(solver='CVXOPT')
+        prob.solve(solver='Clarabel')
     except _cvxpy.error.SolverError as e:
         _warnings.warn("CVXPY failed: %s - diamonddist returning -2!" % str(e))
         return (-2, _np.zeros((dim, dim))) if return_x else -2

pyproject.toml

@@ -52,8 +52,7 @@ classifiers=[
 
 [project.optional-dependencies]
 diamond_norm = [
-    'cvxopt',
-    'cvxpy'
+    'cvxpy>=1.4.0'
 ]
 evolutionary_optimization = ['deap']
 extensions = ['cython']