docs: def add_gt_proposals(self, proposals, targets):
          """
          Arguments:
              proposals: list[BoxList]
              targets: list[BoxList]
          """
          # Get the device we're operating on
          device = proposals[0].bbox.device
  
          gt_boxes = [target.copy_with_fields([]) for target in targets]
  
          # later cat of bbox requires all fields to be present for all bbox
          # so we need to add a dummy for objectness that's missing
          for gt_box in gt_boxes:
              gt_box.add_field("objectness", torch.ones(len(gt_box), device=device))
  
          proposals = [
              cat_boxlist((proposal, gt_box))
              for proposal, gt_box in zip(proposals, gt_boxes)
          ]
  
          return proposals