refactor(tests): update processor test assertions to reflect new preprocessor and postprocessor names (#1869)

- Changed assertions in multiple processor test files to verify the updated names from "robot_preprocessor" and "robot_postprocessor" to "policy_preprocessor" and "policy_postprocessor" for consistency with recent refactoring.

tests/processor/test_pi0_processor.py

@@ -110,8 +110,8 @@ def test_make_pi0_processor_basic():
         )
 
     # Check processor names
-    assert preprocessor.name == "robot_preprocessor"
-    assert postprocessor.name == "robot_postprocessor"
+    assert preprocessor.name == "policy_preprocessor"
+    assert postprocessor.name == "policy_postprocessor"
 
     # Check steps in preprocessor
     assert len(preprocessor.steps) == 6