sv.Detections has exactly N of each member, except for `tracker_id`. about supervision

[LinasKo]

I'm heavily in favour of 1. The steps for this would be:

• Find, learn of all places where tracker_id is used.
• Modify the core of ByteTrack - if there is a detection but there's no tracker - instead of returning nothing, return -1. Make sure the length of tracker_id matches the length of detections being returned.
• Think a bit how this affects case where we deliberately hide uncertain trackers - this would be introduced as part of #1076.
• Propagate the changes in the core of ByteTrack, to the uses by various components - annotators, examples
• Some tests would be good to have.

This would be a draft PR until #1076 is merged. This PR new should remove the Detections.empty call from it.

[LinasKo]

Example: line_zone.py:trigger() checks if iterating over tracker_id array produces None

Related: Test case in #1206 checks it too.

[LinasKo]

Example: smoother.py:update_with_detections() checks if iterating over tracker_id array produces None