fix(items): safe cast in _try_return_to_chest, typed chest state param, object_states reset

- Replace unsafe direct cast in HoldableItem._try_return_to_chest() with guarded as-cast
- Type set_chest_state() parameter as Array[String] to match RoomChest._get_spawned_ids()
- Add else-branch in apply_save_data() to reset _object_states when key absent
- Rename test_save_data_has_version_two to test_save_data_has_version_three

scripts/objects/holdable_item.gd

@@ -43,7 +43,10 @@ func _try_return_to_chest() -> bool:
 		return false
 	if global_position.distance_to(home_chest.global_position) >= CHEST_RETURN_RADIUS:
 		return false
-	(home_chest as RoomChest).receive_item(self)
+	var chest: RoomChest = home_chest as RoomChest
+	if chest == null:
+		return false
+	chest.receive_item(self)
 	return true