Replace deprecated Numpy's product by prod (#347)

Replace the deprecated `numpy.product` function for `numpy.prod`.
`numpy.product` is deprecated as of NumPy 1.25.0, and will be removed in
NumPy 2.0.

Author: prisae

discretize/tests.py

@@ -845,8 +845,8 @@ def random(size, iscomplex):
         return out
 
     # Create random vectors u and v.
-    u = random(np.product(shape_u), complex_u).reshape(shape_u)
-    v = random(np.product(shape_v), complex_v).reshape(shape_v)
+    u = random(np.prod(shape_u), complex_u).reshape(shape_u)
+    v = random(np.prod(shape_v), complex_v).reshape(shape_v)
 
     # Carry out dot product test.
     fwd_u = forward(u)