refactor: Use jax.numpy for JAX backend tensorlib.tolist (#1138)

* Use jax.numpy.tolist to provide the tolist method for the JAX backend
   - Note that NumPy dependency can never be removed as JAX depends on
     NumPy for JAX to NumPy conversion

src/pyhf/tensor/jax_backend.py

@@ -179,8 +179,8 @@ def conditional(self, predicate, true_callable, false_callable):
 
     def tolist(self, tensor_in):
         try:
-            return np.asarray(tensor_in).tolist()
-        except AttributeError:
+            return jnp.asarray(tensor_in).tolist()
+        except TypeError:
             if isinstance(tensor_in, list):
                 return tensor_in
             raise