Update test_calculator.py to clarify raw_case fixture usage

Added a comment to the raw_case parameter in the test_calculator_output_matches_legacy function to indicate its purpose as a fixture. This change aims to improve code readability and maintainability by providing clearer context for future developers.

Author: FridrichMethod

tests/test_calculator.py

@@ -16,7 +16,7 @@ def _legacy_variables_from_dataclasses(variables: list[Variable]) -> list[tuple[
 
 
 def test_calculator_output_matches_legacy(
-    raw_case: RawCase,
+    raw_case: RawCase,  # noqa: ARG001 (fixture only; equation/variables derive from it)
     equation,
     variables,
     digits,