animation

[JaskRendix]

PR:

1. Added a check for empty frames sequence: In the __init__ method, a ValueError is raised if the frames sequence is empty. This ensures that the animation token is always initialized with a valid sequence of frames.
2. Added a return type hint for the advance method: The advance method now includes a return type hint, indicating that it returns an AnimationFrame object.
3. Added a docstring for the __lt__ method: The __lt__ method now includes a docstring that explains its purpose and behavior.
4. Added a __repr__ method: The __repr__ method provides a string representation of the AnimationToken object, which can be useful for debugging and logging purposes.