Fix numpy v1.24 compatibility

Numpy v1.24 deprecated ragged arrays unless dtype=object
is passed (numpy/numpy#22004). The SimulationResult class
needs to support different length entries in tout in the
case that these differ across simulations. PySB shouldn't
convert these to a numpy array, instead preferring to
keep them as a list/iterable.

pysb/simulator/base.py

@@ -748,7 +748,7 @@ def __init__(self, simulator, tout, trajectories=None,
             self.run_kwargs = {}
 
         self.squeeze = squeeze
-        self.tout = np.asarray(tout)
+        self.tout = tout
         self._yfull = None
         self.n_sims_per_parameter_set = simulations_per_param_set
         self.pysb_version = PYSB_VERSION