Add frozen combat modelling.

This doesn't do anything yet, but sets up the data model handling for
frozen combat. The next step is to show combat in the map view, since
that will be helpful when debugging the step after that one: resolving
frozen combat.

This would benefit from caching the Shapely data for SAM threat zones.
Right now it's generating them once per tick and the stuttering is
visible at max speed.

https://github.com/dcs-liberation/dcs_liberation/issues/1680

game/debriefing.py

@@ -13,23 +13,23 @@ from typing import (
     Union,
 )
 
-from game.ato.flight import Flight
 from game.dcs.aircrafttype import AircraftType
 from game.dcs.groundunittype import GroundUnitType
 from game.theater import Airfield, ControlPoint
-from game.transfers import CargoShip
-from game.unitmap import (
-    AirliftUnits,
-    Building,
-    ConvoyUnit,
-    FlyingUnit,
-    FrontLineUnit,
-    GroundObjectUnit,
-    UnitMap,
-)
 
 if TYPE_CHECKING:
     from game import Game
+    from game.ato.flight import Flight
+    from game.transfers import CargoShip
+    from game.unitmap import (
+        AirliftUnits,
+        Building,
+        ConvoyUnit,
+        FlyingUnit,
+        FrontLineUnit,
+        GroundObjectUnit,
+        UnitMap,
+    )
 
 DEBRIEFING_LOG_EXTENSION = "log"