Add Cooler, Bag, and compact hotbar systems

items/owned_item.gd

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+class_name OwnedItem
+extends Resource
+
+@export var item_id: StringName
+@export var quantity: int = 1
+
+
+func is_valid() -> bool:
+	return not item_id.is_empty() and quantity > 0
+
+
+func duplicate_record():
+	return duplicate(true)
+
+
+func to_save_dict() -> Dictionary:
+	return {
+		"item_id": String(item_id),
+		"quantity": quantity,
+	}