Calculate how long a string is needed to show a summary string.

        This is not simply the length of the formatted summary string
        since that string might contain ANSI codes.

def summary_width(self):
        """Calculate how long a string is needed to show a summary string.

        This is not simply the length of the formatted summary string
        since that string might contain ANSI codes.
        """
        chunk_counts = [chunk.count for chunk in self._progress_chunks]
        numbers_width = sum(max(1, ceil(log10(count + 1)))
                            for count in chunk_counts)
        separators_with = len(chunk_counts) - 1
        return numbers_width + separators_with