Feat/pipeline add feature contract (#1637)

* Add feature contract to pipelinestep and pipeline

* Add tests

* Add processor tests

* PR feedback

* encorperate pr feedback

* type in doc

* oops

src/lerobot/processor/rename_processor.py

@@ -18,6 +18,7 @@ from typing import Any
 
 import torch
 
+from lerobot.configs.types import PolicyFeature
 from lerobot.processor.pipeline import EnvTransition, ProcessorStepRegistry, TransitionKey
 
 
@@ -53,3 +54,10 @@ class RenameProcessor:
 
     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.
+        - Keys not in `rename_map` remain unchanged.
+        """
+        return {self.rename_map.get(k, k): v for k, v in features.items()}