[Refactor] Performance optimization

- Put download token in memory database
- Accelerate multiple querying in `best_score` table

latest version/server/others.py

@@ -29,12 +29,14 @@ def game_info():
 @auth_required(request)
 @arc_try
 def download_song(user_id):
-    with Connect() as c:
-        x = DownloadList(c, UserOnline(c, user_id))
+    with Connect(in_memory=True) as c:
+        x = DownloadList(c, UserOnline(None, user_id))
         x.song_ids = request.args.getlist('sid')
         x.url_flag = json.loads(request.args.get('url', 'true'))
         if x.url_flag and x.is_limited:
             raise RateLimit('You have reached the download limit.', 903)
+        if x.url_flag:
+            x.clear_download_token()
 
         x.add_songs()
         return success_return(x.urls)