Reset game state on new turn.

This may not be the way to do this long term, but it is how the old map
works so it's at least not a regression. It might be better to generate
events for the between-turn changes in state instead.

https://github.com/dcs-liberation/dcs_liberation/issues/2039

game/sim/gameupdateevents.py

@@ -36,6 +36,7 @@ class GameUpdateEvents:
     updated_control_points: set[int] = field(default_factory=set)
     reset_on_map_center: LatLng | None = None
     game_unloaded: bool = False
+    new_turn: bool = False
     shutting_down: bool = False
 
     @property
@@ -136,6 +137,10 @@ class GameUpdateEvents:
             self.game_unloaded = False
         return self
 
+    def begin_new_turn(self) -> GameUpdateEvents:
+        self.new_turn = True
+        return self
+
     def shut_down(self) -> GameUpdateEvents:
         self.shutting_down = True
         return self