Core, WebHost: lazy-load worlds in unpickler, WebHost and WebHostLib (#2156)

* Core: lazy-load worlds in unpickler

this should hopefully fix customserver's memory consumption

* WebHost: move imports around to save memory in MP

* MultiServer: prefer loading _speedups without pyximport

This saves ~15MB per MP and speeds up module import if it was built in-place.

* Tests: fix tests for changed WebHost imports

* CustomServer: run GC after setup

* CustomServer: cleanup exception handling

WebHost.py

@@ -13,15 +13,6 @@ import Utils
 import settings
 
 Utils.local_path.cached_path = os.path.dirname(__file__) or "."  # py3.8 is not abs. remove "." when dropping 3.8
-
-from WebHostLib import register, cache, app as raw_app
-from waitress import serve
-
-from WebHostLib.models import db
-from WebHostLib.autolauncher import autohost, autogen
-from WebHostLib.lttpsprites import update_sprites_lttp
-from WebHostLib.options import create as create_options_files
-
 settings.no_gui = True
 configpath = os.path.abspath("config.yaml")
 if not os.path.exists(configpath):  # fall back to config.yaml in home
@@ -29,6 +20,9 @@ if not os.path.exists(configpath):  # fall back to config.yaml in home
 
 
 def get_app():
+    from WebHostLib import register, cache, app as raw_app
+    from WebHostLib.models import db
+
     register()
     app = raw_app
     if os.path.exists(configpath) and not app.config["TESTING"]:
@@ -121,6 +115,11 @@ if __name__ == "__main__":
     multiprocessing.freeze_support()
     multiprocessing.set_start_method('spawn')
     logging.basicConfig(format='[%(asctime)s] %(message)s', level=logging.INFO)
+
+    from WebHostLib.lttpsprites import update_sprites_lttp
+    from WebHostLib.autolauncher import autohost, autogen
+    from WebHostLib.options import create as create_options_files
+
     try:
         update_sprites_lttp()
     except Exception as e:
@@ -137,4 +136,5 @@ if __name__ == "__main__":
         if app.config["DEBUG"]:
             app.run(debug=True, port=app.config["PORT"])
         else:
+            from waitress import serve
             serve(app, port=app.config["PORT"], threads=app.config["WAITRESS_THREADS"])