fix: add pre_start() to _IncomingHandler for dingtalk SDK compatibility

The dingtalk-stream SDK calls pre_start() on every registered handler
before opening the WebSocket connection. Without this method, the SDK
raises AttributeError and kills the stream connection, causing DingTalk
to be unable to connect via Stream Mode.

gateway/platforms/dingtalk.py

@@ -1395,6 +1395,16 @@ class _IncomingHandler(
         self._adapter = adapter
         self._loop = loop
 
+    def pre_start(self) -> None:
+        """No-op pre-start hook required by dingtalk-stream SDK.
+
+        The SDK calls ``pre_start()`` on every registered handler before
+        opening the WebSocket connection.  Without this method, the SDK
+        raises ``AttributeError: '_IncomingHandler' object has no
+        attribute 'pre_start'`` and kills the stream connection.
+        """
+        return
+
     async def process(self, message: "CallbackMessage"):
         """Called by dingtalk-stream (>=0.20) when a message arrives.