ProductReleaseFileMixin.latest_release_with_download_files is inefficient for projects with many releases

See: https://oops.canonical.com/?oopsid=OOPS-31b11f108e721633529066220ca65fdd

There are possibly multiple problems here, but one that jumps out at me is:

    @cachedproperty
    def latest_release_with_download_files(self):
        """Return the latest release with download files."""
        for series in self.sorted_active_series_list:
            for release in series.releases:
                if len(list(release.files)) > 0:
                    return release
        return None

This needs to be replaced with a more targeted query.