[support-3d] A4. 3D ball-ball detection

[ekiefl]

Category: Detection

Currently a stub: pooltool/evolution/event_based/detect/ball_ball.py:80.

If it ends up being trivial to have a single function that manages both 2D and 3D, then call it _get_next_ball_ball_event, and have two thin wrappers, get_next_ball_ball_event_2d, and get_next_ball_ball_event_3d that the dispatcher EventDetector.get_next_event call conditioned on EventDetector.is_3d.