Get dtypes to use when unpacking sqlite tables as dataframes.

def _df_dtypes(self, table_name, convert_dates):
        """Get dtypes to use when unpacking sqlite tables as dataframes.
        """
        out = self._raw_table_dtypes[table_name]
        if convert_dates:
            out = out.copy()
            for date_column in self._datetime_int_cols[table_name]:
                out[date_column] = datetime64ns_dtype

        return out