refactor(pipeline): minor improvements (#1684)

* chore(pipeline): remove unused features + device torch + envtransition keys

* refactor(pipeline): ImageProcessor & StateProcessor are both implemented directly in VanillaObservationPRocessor

* refactor(pipeline): RenameProcessor now inherits from ObservationProcessor + remove unused code

* test(pipeline): fix broken test after refactors

* docs(pipeline): update docstrings VanillaObservationProcessor

* chore(pipeline): move None check to base pipeline classes

src/lerobot/processor/rename_processor.py

@@ -16,24 +16,21 @@
 from dataclasses import dataclass, field
 from typing import Any
 
-import torch
-
 from lerobot.configs.types import PolicyFeature
-from lerobot.processor.pipeline import EnvTransition, ProcessorStepRegistry, TransitionKey
+from lerobot.processor.pipeline import (
+    ObservationProcessor,
+    ProcessorStepRegistry,
+)
 
 
 @dataclass
 @ProcessorStepRegistry.register(name="rename_processor")
-class RenameProcessor:
+class RenameProcessor(ObservationProcessor):
     """Rename processor that renames keys in the observation."""
 
     rename_map: dict[str, str] = field(default_factory=dict)
 
-    def __call__(self, transition: EnvTransition) -> EnvTransition:
-        observation = transition.get(TransitionKey.OBSERVATION)
-        if observation is None:
-            return transition
-
+    def observation(self, observation):
         processed_obs = {}
         for key, value in observation.items():
             if key in self.rename_map:
@@ -41,20 +38,11 @@ class RenameProcessor:
             else:
                 processed_obs[key] = value
 
-        # Create a new transition with the renamed observation
-        new_transition = transition.copy()
-        new_transition[TransitionKey.OBSERVATION] = processed_obs
-        return new_transition
+        return processed_obs
 
     def get_config(self) -> dict[str, Any]:
         return {"rename_map": self.rename_map}
 
-    def state_dict(self) -> dict[str, torch.Tensor]:
-        return {}
-
-    def load_state_dict(self, state: dict[str, torch.Tensor]) -> None:
-        pass
-
     def feature_contract(self, features: dict[str, PolicyFeature]) -> dict[str, PolicyFeature]:
         """Transforms:
         - Each key in the observation that appears in `rename_map` is renamed to its value.