Use the best aircraft rather than first found.

The priority list was guiding the purchase decision which largely meant
that this was working correctly, but there were suboptimal cases where
the list was being taken in FIFO order by purchased type. This fixes the
search to be locally optimal, although this does still mean that a worse
but closer aircraft will be chosen over a better but slightly farther
away aircraft. We'd need to have a quality vs distance rating to do
better.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/755

gen/flights/ai_flight_planner.py

@@ -162,10 +162,10 @@ class AircraftAllocator:
             if not airfield.is_friendly(self.is_player):
                 continue
             inventory = self.global_inventory.for_control_point(airfield)
-            for aircraft, available in inventory.all_aircraft:
+            for aircraft in types:
                 if not airfield.can_operate(aircraft):
                     continue
-                if aircraft in types and available >= flight.num_aircraft:
+                if inventory.available(aircraft) >= flight.num_aircraft:
                     inventory.remove_aircraft(aircraft, flight.num_aircraft)
                     return airfield, aircraft