sessionOptions.keepAlive
指定以毫秒为单位的保持活动超时。当设置为非零值时，会自动发送 PING 帧以在空闲超时触发前保持连接活动。该值应小于有效的空闲超时（maxIdleTimeout 传输参数），以便有用。
🌐 Specifies the keep-alive timeout in milliseconds. When set to a non-zero
value, PING frames will be sent automatically to keep the connection alive
before the idle timeout fires. The value should be less than the effective
idle timeout (maxIdleTimeout transport parameter) to be useful.