_cubes(self):         mesh_0 = generate_box_mesh(                 np.array([0, 0, 0]), np.array([0, 0, 0]))         mesh_0 = generate_box_mesh(                 np.array([0, 0, 0]), np.array([0, 0, 0]))         mesh = merge_meshes((mesh_0, mesh_0))         outer_hull