fix more bugs in normalization

lerobot/common/datasets/abstract.py

@@ -54,7 +54,7 @@ class AbstractExperienceReplay(TensorDictReplayBuffer):
         return {
             ("observation", "state"): "b c -> 1 c",
             ("observation", "image"): "b c h w -> 1 c 1 1",
-            "action": "b c -> 1 c",
+            ("action",): "b c -> 1 c",
         }
 
     @property
@@ -73,8 +73,12 @@ class AbstractExperienceReplay(TensorDictReplayBuffer):
     def num_episodes(self) -> int:
         return len(self._storage._storage["episode"].unique())
 
+    @property
+    def transform(self):
+        return self._transform
+
     def set_transform(self, transform):
-        self.transform = transform
+        self._transform = transform
 
     def compute_or_load_stats(self, num_batch=100, batch_size=32) -> TensorDict:
         stats_path = self.data_dir / "stats.pth"