Fix merged classvars in UnitType descendants.

```
>>> class Foo:
...     bar = 0
...     @classmethod
...     def set_bar(cls, v):
...             cls.bar = v
...
>>> class Bar(Foo):
...     ...
...
>>> Bar.set_bar(1)
>>> Bar.bar
1
>>> Foo.bar
0
>>> class Foo:
...     bar = {}
...     @classmethod
...     def add(cls, k, v):
...             cls.bar[k] = v
...
>>> class Bar(Foo):
...     pass
...
>>> Bar.add(0, 1)
>>> Bar.bar
{0: 1}
>>> Foo.bar
{0: 1}
```

The collections are copied by reference into the descendants, whereas
_loaded is copied by value, so that one can stay. Before this patch,
every subtype was loading because _loaded was set per subclass, but they
were all registering with a common collection defined by UnitType rather
than their own class.

game/dcs/aircrafttype.py

@@ -1,10 +1,11 @@
 from __future__ import annotations
 
 import logging
+from collections import defaultdict
 from dataclasses import dataclass
 from functools import cached_property
 from pathlib import Path
-from typing import Any, Dict, Iterator, Optional, TYPE_CHECKING, Type
+from typing import Any, ClassVar, Dict, Iterator, Optional, TYPE_CHECKING, Type
 
 import yaml
 from dcs.helicopters import helicopter_map
@@ -197,6 +198,16 @@ class AircraftType(UnitType[Type[FlyingType]]):
     # when no TGP is mounted on any station.
     has_built_in_target_pod: bool
 
+    _by_name: ClassVar[dict[str, AircraftType]] = {}
+    _by_unit_type: ClassVar[dict[type[FlyingType], list[AircraftType]]] = defaultdict(
+        list
+    )
+
+    @classmethod
+    def register(cls, unit_type: AircraftType) -> None:
+        cls._by_name[unit_type.name] = unit_type
+        cls._by_unit_type[unit_type.dcs_unit_type].append(unit_type)
+
     @property
     def flyable(self) -> bool:
         return self.dcs_unit_type.flyable
@@ -321,17 +332,13 @@ class AircraftType(UnitType[Type[FlyingType]]):
     def named(cls, name: str) -> AircraftType:
         if not cls._loaded:
             cls._load_all()
-        unit = cls._by_name[name]
+        return cls._by_name[name]
-        assert isinstance(unit, AircraftType)
-        return unit
 
     @classmethod
     def for_dcs_type(cls, dcs_unit_type: Type[FlyingType]) -> Iterator[AircraftType]:
         if not cls._loaded:
             cls._load_all()
-        for unit in cls._by_unit_type[dcs_unit_type]:
+        yield from cls._by_unit_type[dcs_unit_type]
-            assert isinstance(unit, AircraftType)
-            yield unit
 
     @staticmethod
     def each_dcs_type() -> Iterator[Type[FlyingType]]:

game/dcs/groundunittype.py

@@ -1,9 +1,10 @@
 from __future__ import annotations
 
 import logging
+from collections import defaultdict
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Any, Iterator, Optional, Type
+from typing import Any, ClassVar, Iterator, Optional, Type
 
 import yaml
 from dcs.unittype import VehicleType
@@ -59,21 +60,27 @@ class GroundUnitType(UnitType[Type[VehicleType]]):
     # Some units like few Launchers have to be placed backwards to be able to fire.
     reversed_heading: bool = False
 
+    _by_name: ClassVar[dict[str, GroundUnitType]] = {}
+    _by_unit_type: ClassVar[
+        dict[type[VehicleType], list[GroundUnitType]]
+    ] = defaultdict(list)
+
+    @classmethod
+    def register(cls, unit_type: GroundUnitType) -> None:
+        cls._by_name[unit_type.name] = unit_type
+        cls._by_unit_type[unit_type.dcs_unit_type].append(unit_type)
+
     @classmethod
     def named(cls, name: str) -> GroundUnitType:
         if not cls._loaded:
             cls._load_all()
-        unit = cls._by_name[name]
+        return cls._by_name[name]
-        assert isinstance(unit, GroundUnitType)
-        return unit
 
     @classmethod
     def for_dcs_type(cls, dcs_unit_type: Type[VehicleType]) -> Iterator[GroundUnitType]:
         if not cls._loaded:
             cls._load_all()
-        for unit in cls._by_unit_type[dcs_unit_type]:
+        yield from cls._by_unit_type[dcs_unit_type]
-            assert isinstance(unit, GroundUnitType)
-            yield unit
 
     @staticmethod
     def each_dcs_type() -> Iterator[Type[VehicleType]]:

game/dcs/shipunittype.py

@@ -1,9 +1,10 @@
 from __future__ import annotations
 
 import logging
+from collections import defaultdict
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Iterator, Type
+from typing import ClassVar, Iterator, Type
 
 import yaml
 from dcs.ships import ship_map
@@ -15,21 +16,27 @@ from game.dcs.unittype import UnitType
 
 @dataclass(frozen=True)
 class ShipUnitType(UnitType[Type[ShipType]]):
+    _by_name: ClassVar[dict[str, ShipUnitType]] = {}
+    _by_unit_type: ClassVar[dict[type[ShipType], list[ShipUnitType]]] = defaultdict(
+        list
+    )
+
+    @classmethod
+    def register(cls, unit_type: ShipUnitType) -> None:
+        cls._by_name[unit_type.name] = unit_type
+        cls._by_unit_type[unit_type.dcs_unit_type].append(unit_type)
+
     @classmethod
     def named(cls, name: str) -> ShipUnitType:
         if not cls._loaded:
             cls._load_all()
-        unit = cls._by_name[name]
+        return cls._by_name[name]
-        assert isinstance(unit, ShipUnitType)
-        return unit
 
     @classmethod
     def for_dcs_type(cls, dcs_unit_type: Type[ShipType]) -> Iterator[ShipUnitType]:
         if not cls._loaded:
             cls._load_all()
-        for unit in cls._by_unit_type[dcs_unit_type]:
+        yield from cls._by_unit_type[dcs_unit_type]
-            assert isinstance(unit, ShipUnitType)
-            yield unit
 
     @staticmethod
     def each_dcs_type() -> Iterator[Type[ShipType]]:

game/dcs/unittype.py

@@ -1,10 +1,9 @@
 from __future__ import annotations
 
 from abc import ABC
-from collections import defaultdict
 from dataclasses import dataclass
 from functools import cached_property
-from typing import Any, ClassVar, Generic, Iterator, Type, TypeVar
+from typing import ClassVar, Generic, Iterator, Self, Type, TypeVar
 
 from dcs.unittype import UnitType as DcsUnitType
 
@@ -25,10 +24,6 @@ class UnitType(ABC, Generic[DcsUnitTypeT]):
     price: int
     unit_class: UnitClass
 
-    _by_name: ClassVar[dict[str, UnitType[Any]]] = {}
-    _by_unit_type: ClassVar[dict[Type[DcsUnitType], list[UnitType[Any]]]] = defaultdict(
-        list
-    )
     _loaded: ClassVar[bool] = False
 
     def __str__(self) -> str:
@@ -39,16 +34,15 @@ class UnitType(ABC, Generic[DcsUnitTypeT]):
         return self.dcs_unit_type.id
 
     @classmethod
-    def register(cls, unit_type: UnitType[Any]) -> None:
+    def register(cls, unit_type: Self) -> None:
-        cls._by_name[unit_type.name] = unit_type
-        cls._by_unit_type[unit_type.dcs_unit_type].append(unit_type)
-
-    @classmethod
-    def named(cls, name: str) -> UnitType[Any]:
         raise NotImplementedError
 
     @classmethod
-    def for_dcs_type(cls, dcs_unit_type: DcsUnitTypeT) -> Iterator[UnitType[Any]]:
+    def named(cls, name: str) -> Self:
+        raise NotImplementedError
+
+    @classmethod
+    def for_dcs_type(cls, dcs_unit_type: DcsUnitTypeT) -> Iterator[Self]:
         raise NotImplementedError
 
     @staticmethod
@@ -56,7 +50,7 @@ class UnitType(ABC, Generic[DcsUnitTypeT]):
         raise NotImplementedError
 
     @classmethod
-    def _each_variant_of(cls, unit: DcsUnitTypeT) -> Iterator[UnitType[Any]]:
+    def _each_variant_of(cls, unit: DcsUnitTypeT) -> Iterator[Self]:
         raise NotImplementedError
 
     @classmethod