Improve prioritization of garrison targeting.

Garrison groups should be preferred with the following priority:

1. Groups blocking base capture
2. Groups at bases connected to an active front line
3. Rear guard units

Previously they were being prioritized based on the distance to the
closest friendy control point, which is similar to this but an
aggressively placed carrier could throw it off.

game/commander/tasks/compound/attackgarrisons.py

@@ -7,5 +7,5 @@ from game.htn import CompoundTask, Method
 
 class AttackGarrisons(CompoundTask[TheaterState]):
     def each_valid_method(self, state: TheaterState) -> Iterator[Method[TheaterState]]:
-        for garrison in state.enemy_garrisons:
+        for garrison in state.enemy_garrisons.in_priority_order:
             yield [PlanBai(garrison)]

game/commander/tasks/primitive/bai.py

@@ -17,7 +17,7 @@ class PlanBai(PackagePlanningTask[VehicleGroupGroundObject]):
         return self.target_area_preconditions_met(state)
 
     def apply_effects(self, state: TheaterState) -> None:
-        state.enemy_garrisons.remove(self.target)
+        state.enemy_garrisons.eliminate(self.target)
 
     def propose_flights(self, doctrine: Doctrine) -> None:
         self.propose_flight(FlightType.BAI, 2, doctrine.mission_ranges.offensive)