Add fraction, single_cls and classes to RTDETRDataset (#17633)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/models/rtdetr/train.py

@@ -68,8 +68,11 @@ class RTDETRTrainer(DetectionTrainer):
             hyp=self.args,
             rect=False,
             cache=self.args.cache or None,
+            single_cls=self.args.single_cls or False,
             prefix=colorstr(f"{mode}: "),
+            classes=self.args.classes,
             data=self.data,
+            fraction=self.args.fraction if mode == "train" else 1.0,
         )
 
     def get_validator(self):