Use the actual Country type instead of the name.

We want other pieces of country information (in particular the short
names). This cleans up a lot of code anyway.

As an added bonus, this now catches squadrons that used invalid names
which would previously be passed through to pydcs and... then I don't
know what would happen.

game/missiongenerator/convoygenerator.py

@@ -70,13 +70,11 @@ class ConvoyGenerator:
         units: dict[GroundUnitType, int],
         for_player: bool,
     ) -> VehicleGroup:
-        country = self.mission.country(self.game.coalition_for(for_player).country_name)
-
         unit_types = list(units.items())
         main_unit_type, main_unit_count = unit_types[0]
 
         group = self.mission.vehicle_group(
-            country,
+            self.game.coalition_for(for_player).faction.country,
             name,
             main_unit_type.dcs_unit_type,
             position=position,