Mark unused action arg in sim_fn to satisfy pylint

The simulator callback signature must match StepSimulatorFn's
(state, action, params) shape even though apply_rules doesn't use
the action. Renaming to _action signals intent and silences pylint's
unused-argument check.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yichao-liang

predicators/approaches/agent_sim_learning_approach.py

@@ -323,8 +323,8 @@ def _fit_parameters(
         precomputing avoids re-running it inside the MCMC inner loop.
         """
 
-        def sim_fn(state: State, action: Action, params: Dict[str,
-                                                              float]) -> Dict:
+        def sim_fn(state: State, _action: Action, params: Dict[str,
+                                                               float]) -> Dict:
             return apply_rules(state, rules, params)
 
         noise_sigma = 0.05  # matches fit_params default