reset waitingHeartbeat flag in Close method

Add missing reset of waitingHeartbeat flag when closing the client.
This prevents stale state from persisting during reconnection attempts,
which was causing abnormal heartbeat behavior after reconnections.

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>

Author: zhaojh329

rtty.go

@@ -221,6 +221,7 @@ func (cli *RttyClient) Register() error {
 
 func (cli *RttyClient) Close() {
 	cli.mu.Lock()
+	cli.waitingHeartbeat = false
 	if cli.heartbeatTimer != nil {
 		cli.heartbeatTimer.Stop()
 		cli.heartbeatTimer = nil