[chore][conversation][bind memory_md_path to a local so pyre keeps the narrowing]

Author: ayaangazali

swarms/structs/conversation.py

@@ -664,21 +664,19 @@ def rollback(self, checkpoint: Tuple[int, int]):
         del self.conversation_history[length:]
         self._str_cache = None
 
-        if not self.memory_md_path:
+        path = self.memory_md_path
+        if not path:
             return
 
         try:
             with self._memory_md_lock:
                 if (
-                    os.path.exists(self.memory_md_path)
-                    and os.path.getsize(self.memory_md_path)
-                    > memory_md_size
+                    os.path.exists(path)
+                    and os.path.getsize(path) > memory_md_size
                 ):
-                    os.truncate(self.memory_md_path, memory_md_size)
+                    os.truncate(path, memory_md_size)
         except Exception as e:
-            logger.error(
-                f"Failed to roll back {self.memory_md_path}: {e}"
-            )
+            logger.error(f"Failed to roll back {path}: {e}")
 
     def update(self, index: str, role, content):
         """Update a message in the conversation history.