refactor(migrate_policy_normalization): Enhance preprocessor and postprocessor structure

- Introduced RenameProcessor in the preprocessor to handle renaming features.
- Combined input and output features in a single NormalizerProcessor for improved efficiency.
- Updated RobotProcessor initialization to clarify step naming for preprocessor and postprocessor.
- Added DeviceProcessor to both preprocessor and postprocessor for better device management.

src/lerobot/processor/migrate_policy_normalization.py

@@ -47,8 +47,10 @@ from safetensors.torch import load_file as load_safetensors
 
 from lerobot.configs.types import FeatureType, NormalizationMode, PolicyFeature
 from lerobot.processor.batch_processor import ToBatchProcessor
+from lerobot.processor.device_processor import DeviceProcessor
 from lerobot.processor.normalize_processor import NormalizerProcessor, UnnormalizerProcessor
 from lerobot.processor.pipeline import RobotProcessor
+from lerobot.processor.rename_processor import RenameProcessor
 
 # Policy type to class mapping
 POLICY_CLASSES = {
@@ -410,18 +412,23 @@ def main():
 
     # Create preprocessor with two normalizers (following the pattern from processor factories)
     preprocessor_steps = [
-        NormalizerProcessor(features=input_features, norm_map=norm_map, stats=stats),
-        NormalizerProcessor(features=output_features, norm_map=norm_map, stats=stats),
+        RenameProcessor(rename_map={}),
+        NormalizerProcessor(
+            features={**input_features, **output_features},
+            norm_map=norm_map,
+            stats=stats,
+        ),
         ToBatchProcessor(),
+        DeviceProcessor(device=policy_config.device),
     ]
-    preprocessor = RobotProcessor(preprocessor_steps, name="preprocessor")
+    preprocessor = RobotProcessor(steps=preprocessor_steps, name="robot_preprocessor")
 
     # Create postprocessor with unnormalizer for outputs only
     postprocessor_steps = [
+        DeviceProcessor(device="cpu"),
         UnnormalizerProcessor(features=output_features, norm_map=norm_map, stats=stats),
-        ToBatchProcessor(),
     ]
-    postprocessor = RobotProcessor(postprocessor_steps, name="postprocessor")
+    postprocessor = RobotProcessor(steps=postprocessor_steps, name="robot_postprocessor")
 
     # Determine hub repo ID if pushing to hub
     if args.push_to_hub: