fix(processor): specialized processors respect contract by raising if none (#1909)

* fix(processor): specialized processor now raise

* test(processor): fix tests for now raise specialized processors

* test(processor): use identity in newly introduced pipeline

tests/processor/test_observation_processor.py

@@ -136,7 +136,7 @@ def test_none_observation():
     """Test processor with None observation."""
     processor = VanillaObservationProcessorStep()
 
-    transition = create_transition()
+    transition = create_transition(observation={})
     result = processor(transition)
 
     assert result == transition