docs: def invertible_flatten2_numpy(unflat_arrs, axis=0):
      """ more numpy version
  
      TODO: move to vtool
  
      Args:
          unflat_arrs (list):  list of ndarrays
  
      Returns:
          tuple: (flat_list, cumlen_list)
  
      CommandLine:
          python -m utool.util_list --test-invertible_flatten2_numpy
  
      Example:
          >>> # ENABLE_DOCTET
          >>> from utool.util_list import *  # NOQA
          >>> unflat_arrs = [np.array([1, 2, 1]), np.array([5, 9]), np.array([4])]
          >>> (flat_list, cumlen_list) = invertible_flatten2_numpy(unflat_arrs)
          >>> result = str((flat_list, cumlen_list))
          >>> print(result)
          (array([1, 2, 1, 5, 9, 4]), array([3, 5, 6]))
      """
      cumlen_list = np.cumsum([arr.shape[axis] for arr in unflat_arrs])
      flat_list = np.concatenate(unflat_arrs, axis=axis)
      return flat_list, cumlen_list