`dreem.io` class functions for creating dummy data

[aaprasad]

It might be useful to have class functions to create dummy data using dreem.io.Frame, dreem.io.Instance, and dreem.io.AssociationMatirx

eg

class Instance:
    @classmethod
     def dummy(cls, gt_track_id=0, pred_track_id=-1, crop_size=64, feature_dim=128, track_score=-1.0, device="cpu"):
            return cls(gt_track_id=gt_track_id,
                              pred_track_id=pred_track_id,
                              crop=torch.randn(1, 3, cropsize),
                              bbox=torch.rand(1,1,4) * cropsize,
                              features=torch.randn(1, feature_dim),
                              track_score=track_score,
                              emb={"pos": torch.randn(1,feature_dim), "temp": torch.randn(1, feature_dim)},
                              device=device
           )

class Frame
    @classmethod
     def dummy(cls, frame_id=0, video_id=0, n_instances=2, img_shape=(3,256,256))
            return cls(frame_id=frame_id, video_id=video_id, img_shape=img_shape, instances = [Instance.dummy(gt_track_id=i) for i in range(n_instances)])

class AssociationMatrix:
      @classmethod
      def dummy(cls, n_ref, n_query):
           return cls(torch.randn(n_query, n_ref), ref_instances = [Instance.dummy(gt_track_id=i, pred_track_id=i) for i in range(n_ref), query_instances = [Instance.dummy(gt_track_id=i) for i in range(n_query)])