Move mission generation code into game.

Operation has been renamed MissionGenerator and is no longer a static
class.

game/ato/flightwaypoint.py

@@ -1,14 +1,18 @@
+from __future__ import annotations
+
 from datetime import timedelta
-from typing import Optional, Sequence, Union
+from typing import Optional, Sequence, TYPE_CHECKING, Union
 
 from dcs import Point
 from dcs.point import MovingPoint, PointAction
 from dcs.unit import Unit
 
-from game.theater import ControlPoint, MissionTarget
 from game.utils import Distance, meters
 from game.ato.flightwaypointtype import FlightWaypointType
 
+if TYPE_CHECKING:
+    from game.theater import ControlPoint, MissionTarget
+
 
 class FlightWaypoint:
     def __init__(