Optimizations

too slow:

    vtu = vtu.extract_cells([
        np.all(vtu.cell[i].points[:, 0] >= repo_x_bounds[0]) &
        np.all(vtu.cell[i].points[:, 0] <= repo_x_bounds[1]) 
        for i in range(vtu.n_cells)])

in crop_repo.py

testcase: results/mesh/3D/Salz-Kissen_prism-id_12-xres_136/glacialcycle/simTH/repo_surf.vtu, results/mesh/3D/Salz-Kissen_prism-id_12-xres_136/glacialcycle/simTH/repo.vtu