Perf: vectorize _get_pairwise_iou with a joint bincount
#837
| Job | Run time |
|---|---|
| 5m 24s | |
| 11m 29s | |
| 7m 20s | |
| 5m 58s | |
| 6m 44s | |
| 16m 57s | |
| 7m 18s | |
| 46m 46s | |
| 42m 10s | |
| 27m 57s | |
| 13m 43s | |
| 7m 21s | |
| 7m 39s | |
| 8m 0s | |
| 8m 46s | |
| 7m 42s | |
| 3h 51m 14s |