improvement: 设置websocket三小时连接

src/main/java/nju/seec/helper/controller/websocket/CommentWebsocket.java

@@ -30,6 +30,8 @@ public class CommentWebsocket {
 
     @OnOpen
     public void onOpen(Session session, @PathParam("slideId") Integer slideId) {
+        // 3小时有效期
+        session.setMaxIdleTimeout(3 * 60 * 60 * 1000);
         this.session = session;
         this.slideId = slideId;
         if (COMMENT_WEBSOCKET_MAP.get(slideId) == null) {