Refactor Suno module: imports, method parameters, and exception handling

- Delete files: `examples/custom_song.mp3`, `examples/intrumental.mp3`, `examples/custom_lyrics.ipynb`, `examples/song.mp3`, `examples/song.ipynb`, `examples/intrumental.ipynb`
- Update `suno.py`:
  - Import `Union` type from `typing` module
  - Modify `get_songs` and `save_songs` methods to accept additional parameters for tags, title, and is_custom
  - Add empty line between `get_songs` and `save_songs` methods
  - Modify `save_songs` method to handle empty song names by setting it to "Untitled"
  - Modify `get_auth_token` method to handle session id not obtained
  - Modify `get_songs` method to handle not ok response by raising exception