Properly handle ball occlusion in vision

[kylestach]

Description

If the ball is occluded, we shouldn't say that it has disappeared. Particularly if it's in the mouth of one of our robots.

This was implemented in a hacky way here: 509ffdb#diff-b5c8fd4df67237c490348588e90810a403f23b0a62dd71c12ef35462fe8a7f44R39-R55, but we should go back and implement it properly.

Requirements

• When the ball is occluded but in our mouth, we know where it is (easy, implemented in the linked PR).
• When a potential ball's position is occluded, we don't kill it as an estimate unless there are more likely estimates (harder).

Design

Not yet completed.