The data types of the aux data for the BaseSparseNDArray.

def _aux_types(self):
        """The data types of the aux data for the BaseSparseNDArray.
        """
        aux_types = []
        num_aux = self._num_aux
        for i in range(num_aux):
            aux_types.append(self._aux_type(i))
        return aux_types