feat(graders): add 0.0-1.0 clamp and round to easy_grader output

graders/easy_grader.py

@@ -8,4 +8,7 @@ def grade_easy(history: list[dict]) -> float:
     
     success_rates = [h.get("attack_success_estimate", 0.0) for h in history]
     max_success = max(success_rates)
-    return max_success
+    
+    # 0.0 - 1.0 clamp and round
+    score = min(1.0, max(0.0, max_success))
+    return round(score, 4)