MultiServer, customserver, CI, Test: Fix problems in room hosting and test/simulate it (#3464)

* Test: add hosting simulation test

* WebHost: add weak typing to get_app()

* MultiServer: add typing to auto_saver_thread

* MultiServer: don't cancel task, properly end it

* customserver: stop auto-save thread from saving after shutdown

and make sure it stops, another potential memory leak

* MultiServer, customserver: make datapackage small again

* customserver: collect/finish room tasks

Hopefully fixes the memory leak we are seeing

* CI: test hosting

* Test: hosting: verify autohoster saves on Ctrl+C

* customserver: save when stopping via Ctrl+C

WebHost.py

@@ -12,6 +12,9 @@ ModuleUpdate.update()
 import Utils
 import settings
 
+if typing.TYPE_CHECKING:
+    from flask import Flask
+
 Utils.local_path.cached_path = os.path.dirname(__file__) or "."  # py3.8 is not abs. remove "." when dropping 3.8
 settings.no_gui = True
 configpath = os.path.abspath("config.yaml")
@@ -19,7 +22,7 @@ if not os.path.exists(configpath):  # fall back to config.yaml in home
     configpath = os.path.abspath(Utils.user_path('config.yaml'))
 
 
-def get_app():
+def get_app() -> "Flask":
     from WebHostLib import register, cache, app as raw_app
     from WebHostLib.models import db