refactor(processors): add transform_features method to various processors (#1843)

src/lerobot/processor/device_processor.py

@@ -18,6 +18,7 @@ from typing import Any
 
 import torch
 
+from lerobot.configs.types import PolicyFeature
 from lerobot.processor.core import EnvTransition, TransitionKey
 from lerobot.processor.pipeline import ProcessorStep, ProcessorStepRegistry
 from lerobot.utils.utils import get_safe_torch_device
@@ -127,3 +128,6 @@ class DeviceProcessor(ProcessorStep):
     def get_config(self) -> dict[str, Any]:
         """Return configuration for serialization."""
         return {"device": self.device, "float_dtype": self.float_dtype}
+
+    def transform_features(self, features: dict[str, PolicyFeature]) -> dict[str, PolicyFeature]:
+        return features