Fix transport leak in ConfigNodeClient during leader redirect (#17631)

Author: CRZbulabula

iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/client/ConfigNodeClient.java

@@ -265,6 +265,10 @@ public ConfigNodeClient(
   }
 
   public void connect(TEndPoint endpoint, int timeoutMs) throws TException {
+    // Close existing transport before reassigning to prevent connection leaks.
+    if (transport != null) {
+      transport.close();
+    }
     transport =
         commonConfig.isEnableInternalSSL()
             ? DeepCopyRpcTransportFactory.INSTANCE.getTransport(
@@ -327,10 +331,6 @@ private void tryToConnect(int timeoutMs) throws TException {
       }
     }
 
-    if (transport != null) {
-      transport.close();
-    }
-
     for (int tryHostNum = 0; tryHostNum < configNodes.size(); tryHostNum++) {
       cursor = (cursor + 1) % configNodes.size();
       TEndPoint tryEndpoint = configNodes.get(cursor);