Fix Item class issues

Fixes #405

steam/ext/csgo/backpack.py

@@ -143,10 +143,11 @@ def __repr__(self) -> str:
         return f"<{self.__class__.__name__} id={self.id} position={self.position}>"
 
 
-class CasketItem(BaseItem):
+@BaseItem.register
+class CasketItem(BaseItem if TYPE_CHECKING else object):
     """Represents an item in a :class:`Casket`."""
 
-    __slots__ = ("_casket_id",)
+    __slots__ = (*BaseItem.SLOTS, "_casket_id")
     _casket_id: AssetID
 
     @property
@@ -162,10 +163,8 @@ def __repr__(self) -> str:
         return f"<{self.__class__.__name__} id={self.id} casket={self.casket}>"
 
 
-@dataclass(repr=False)
-class BaseInspectedItem:
-    """Represents an item received after inspecting an item."""
-
+@dataclass
+class _BaseInspectedItem(metaclass=ABCMeta):
     __slots__ = SLOTS = (
         "id",
         "def_index",
@@ -221,11 +220,21 @@ def __repr__(self) -> str:
         return f"<{self.__class__.__name__} id={self.id}>"
 
 
+@dataclass(repr=False)
+@_BaseInspectedItem.register
+class BaseInspectedItem(_BaseInspectedItem if TYPE_CHECKING else object, metaclass=ABCMeta):
+    """Represents an item received after inspecting an item."""
+
+    __slots__ = _BaseInspectedItem.SLOTS
+    __annotations__ = _BaseInspectedItem.__annotations__
+
+
 OwnerT = TypeVar("OwnerT", bound="PartialUser", default="BaseUser", covariant=True)
 
 
-class InspectedItem(Item[OwnerT], BaseInspectedItem):
-    __slots__ = BaseInspectedItem.SLOTS
+@BaseInspectedItem.register
+class InspectedItem(Item[OwnerT], _BaseInspectedItem):
+    __slots__ = _BaseInspectedItem.SLOTS
 
 
 F = TypeVar("F", bound=Callable[..., object])

tests/unit/test_ext_csgo.py

@@ -1,4 +1,17 @@
+from unittest.mock import MagicMock
+
 from steam.ext import csgo
+from steam.protobufs.econ import Asset, ItemDescription
 
 client = csgo.Client()
 bot = csgo.Bot(command_prefix="!")
+
+
+def test_item_construction():
+    item = csgo.BackpackItem(MagicMock(), Asset(), ItemDescription(), MagicMock())
+    assert csgo.BackpackItem.__slots__
+    for attr in csgo.BackpackItem.__slots__:
+        setattr(item, attr, MagicMock())
+    csgo.BaseInspectedItem(*(MagicMock(),) * len(csgo.BaseInspectedItem.__slots__))
+    for attr in csgo.CasketItem.__slots__:
+        setattr(csgo.CasketItem(), attr, MagicMock())