ultralytics 8.0.43 optimized Results class and fixes (#1069)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Alexander Duda <Alexander.Duda@me.com>
Co-authored-by: Laughing <61612323+Laughing-q@users.noreply.github.com>

ultralytics/yolo/engine/trainer.py

@@ -243,6 +243,8 @@ class BaseTrainer:
             metric_keys = self.validator.metrics.keys + self.label_loss_items(prefix='val')
             self.metrics = dict(zip(metric_keys, [0] * len(metric_keys)))  # TODO: init metrics for plot_results()?
             self.ema = ModelEMA(self.model)
+            if self.args.plots:
+                self.plot_training_labels()
         self.resume_training(ckpt)
         self.scheduler.last_epoch = self.start_epoch - 1  # do not move
         self.run_callbacks('on_pretrain_routine_end')
@@ -501,6 +503,9 @@ class BaseTrainer:
     def plot_training_samples(self, batch, ni):
         pass
 
+    def plot_training_labels(self):
+        pass
+
     def save_metrics(self, metrics):
         keys, vals = list(metrics.keys()), list(metrics.values())
         n = len(metrics) + 1  # number of cols