refactor(processor): improve processor pipeline typing with generic type (#1810)

* refactor(processor): introduce generic type for to_output

- Always return `TOutput`
- Remove `_prepare_transition`, so `__call__` now always returns `TOutput`
- Update tests accordingly
- This refactor paves the way for adding settings for `to_transition` and `to_output` in `make_processor` and the post-processor

* refactor(processor): consolidate ProcessorKwargs usage across policies

- Removed the ProcessorTypes module and integrated ProcessorKwargs directly into the processor pipeline.
- Updated multiple policy files to utilize the new ProcessorKwargs structure for preprocessor and postprocessor arguments.
- Simplified the handling of processor kwargs by initializing them to empty dictionaries when not provided.

tests/processor/test_batch_processor.py

@@ -245,7 +245,7 @@ def test_mixed_observation():
 def test_integration_with_robot_processor():
     """Test ToBatchProcessor integration with RobotProcessor."""
     to_batch_processor = ToBatchProcessor()
-    pipeline = RobotProcessor([to_batch_processor])
+    pipeline = RobotProcessor([to_batch_processor], to_transition=lambda x: x, to_output=lambda x: x)
 
     # Create unbatched observation
     observation = {
@@ -285,7 +285,9 @@ def test_serialization_methods():
 def test_save_and_load_pretrained():
     """Test saving and loading ToBatchProcessor with RobotProcessor."""
     processor = ToBatchProcessor()
-    pipeline = RobotProcessor([processor], name="BatchPipeline")
+    pipeline = RobotProcessor(
+        [processor], name="BatchPipeline", to_transition=lambda x: x, to_output=lambda x: x
+    )
 
     with tempfile.TemporaryDirectory() as tmp_dir:
         # Save pipeline
@@ -296,7 +298,9 @@ def test_save_and_load_pretrained():
         assert config_path.exists()
 
         # Load pipeline
-        loaded_pipeline = RobotProcessor.from_pretrained(tmp_dir)
+        loaded_pipeline = RobotProcessor.from_pretrained(
+            tmp_dir, to_transition=lambda x: x, to_output=lambda x: x
+        )
 
         assert loaded_pipeline.name == "BatchPipeline"
         assert len(loaded_pipeline) == 1
@@ -323,11 +327,13 @@ def test_registry_functionality():
 def test_registry_based_save_load():
     """Test saving and loading using registry name."""
     processor = ToBatchProcessor()
-    pipeline = RobotProcessor([processor])
+    pipeline = RobotProcessor([processor], to_transition=lambda x: x, to_output=lambda x: x)
 
     with tempfile.TemporaryDirectory() as tmp_dir:
         pipeline.save_pretrained(tmp_dir)
-        loaded_pipeline = RobotProcessor.from_pretrained(tmp_dir)
+        loaded_pipeline = RobotProcessor.from_pretrained(
+            tmp_dir, to_transition=lambda x: x, to_output=lambda x: x
+        )
 
         # Verify the loaded processor works
         observation = {