Use explicit reference to app object for server.

I have no idea why the docs think strings are better. pyinstaller wasn't
able to detect the import through the string so the code ended up being
stripped from the package. Use an explicit import to prevent that.

game/server/server.py

@@ -6,6 +6,7 @@ from threading import Thread
 import uvicorn
 from uvicorn import Config
 
+from game.server.app import app
 from game.server.settings import ServerSettings
 
 
@@ -13,7 +14,7 @@ class Server(uvicorn.Server):
     def __init__(self) -> None:
         super().__init__(
             Config(
-                "game.server.app:app",
+                app=app,
                 host=ServerSettings.get().server_bind_address,
                 port=ServerSettings.get().server_port,
                 log_level="info",