refactor(pipeline): feature contract now categorizes between OBS or Action (#1867)

* refactor(processor): signature of transform_features

* refactor(processor): remove prefixes + processor respect new transform_features signature + update test accordingly

* refactor(processor): rename now is only for visual

* refactor(processor): update normalize processor

* refactor(processor): update vanilla processor features

* refactor(processor): feature contract now uses its own enum

* chore(processor): rename renameprocessor

* chore(processor): minor changes

* refactor(processor): add create & change aggregate

* refactor(processor): update aggregate

* refactor(processor): simplify to functions, fix features contracts and rename function

* test(processor): remove to converter tests as now they are very simple

* chore(docs): recover docs joint observations processor

* fix(processor): update RKP

* fix(tests): recv diff test_pipeline

* chore(tests): add docs to test

* chore(processor): leave obs language constant untouched

* fix(processor): correct new shape of feature in crop image processor

tests/processor/test_pi0_processor.py

@@ -30,7 +30,7 @@ from lerobot.processor import (
     EnvTransition,
     NormalizerProcessorStep,
     ProcessorStep,
-    RenameProcessorStep,
+    RenameObservationsProcessorStep,
     TransitionKey,
     UnnormalizerProcessorStep,
 )
@@ -115,7 +115,7 @@ def test_make_pi0_processor_basic():
 
     # Check steps in preprocessor
     assert len(preprocessor.steps) == 6
-    assert isinstance(preprocessor.steps[0], RenameProcessorStep)
+    assert isinstance(preprocessor.steps[0], RenameObservationsProcessorStep)
     assert isinstance(preprocessor.steps[1], AddBatchDimensionProcessorStep)
     assert isinstance(preprocessor.steps[2], Pi0NewLineProcessor)
     # Step 3 would be TokenizerProcessorStep but it's mocked