Add normalization processor and related components

- Introduced `NormalizationProcessor` to handle both observation normalization and action unnormalization.
- Added `ObservationNormalizer` and `ActionUnnormalizer` classes for specific normalization tasks.
- Updated `__init__.py` to include the new `NormalizationProcessor` in the module exports.
- Enhanced `ObservationProcessor` with registration in the `ProcessorStepRegistry` for better modularity.
- Created `RenameProcessor` for renaming keys in observations, improving flexibility in data processing.

src/lerobot/processor/__init__.py

@@ -19,6 +19,7 @@ from .observation_processor import (
     StateProcessor,
 )
 from .pipeline import EnvTransition, ProcessorStep, RobotProcessor
+from .normalize_processor import NormalizationProcessor
 
 __all__ = [
     "RobotProcessor",
@@ -27,4 +28,5 @@ __all__ = [
     "ImageProcessor",
     "StateProcessor",
     "ObservationProcessor",
+    "NormalizationProcessor",
 ]