Update signature for custom_step

src/kimp/kimp.py

@@ -73,7 +73,7 @@ def same_loop(self, c1: CTerm, c2: CTerm) -> bool:
     def can_make_custom_step(self, c: CTerm) -> bool:
         return False
 
-    def custom_step(self, c: CTerm) -> KCFGExtendResult | None:
+    def custom_step(self, c: CTerm, cs: CTermSymbolic) -> KCFGExtendResult | None:
         return None
 
     def is_mergeable(self, c1: CTerm, c2: CTerm) -> bool: