Implement songs in unique dirs

        For deduplication, it is helpful to assume every song is in its own directory. This returns a sequence of songs filtered so

        that there are no two songs sharing the same base dir. This filtering is done arbitrarily.

        """

        raise NotImplementedError()  # TODO Implement

        unique_dirs: set[Path] = set()

        songs_in_unique_dirs: list[Song] = []

        for song in self.songs:

            if song.dir not in unique_dirs:

                songs_in_unique_dirs.append(song)

                unique_dirs.add(song.dir)

        return tuple(songs_in_unique_dirs)