torchmetrics for panoptic and instance segmentation

[rbavery]

there's a lot of recent activity to keep tabs on with torchmetrics

https://github.com/Lightning-AI/metrics/blob/master/src/torchmetrics/detection/panoptic_quality.py - panoptic metric

solution for incorrect mean AP when there are no GT classes but there are predictions (fairly common): Lightning-AI/torchmetrics#1330

improving mAP runtime: Lightning-AI/torchmetrics#1389

it'll probably take some time for these PRs to come together but at least activity is recent. before these are in a release, we probably should use or build on 1330 for correct mAP