refactor: 将多个方法修改为静态方法以提高代码可读性和一致性

src/plugins/PFC/pfc_KnowledgeFetcher.py

@@ -19,7 +19,8 @@ class KnowledgeFetcher:
             request_type="knowledge_fetch",
         )
 
-    async def fetch(self, query: str, chat_history: List[Message]) -> Tuple[str, str]:
+    @staticmethod
+    async def fetch(query: str, chat_history: List[Message]) -> Tuple[str, str]:
         """获取相关知识
 
         Args: