Extra dependencies are imported when loading models via `torch.hub.load`

[chenzhekl]

Contrary to what has been stated in README.md. A bunch of extra dependencies have been imported when loading models via torch.hub.load. For example:

dinov3/dinov3/hub/segmentors.py

Line 10 in 91ffb68

from dinov3.eval.segmentation.models import build_segmentation_decoder

brings in

dinov3/dinov3/eval/utils.py

Line 15 in 91ffb68

from torchmetrics import Metric

This makes the life of people who just want to use the backbone painful.