chore: minor fixes and formatting

dto/cart.py

@@ -1,5 +1,4 @@
 from dataclasses import dataclass
-from typing import Optional
 
 
 @dataclass(frozen=True)
@@ -18,4 +17,4 @@ class CartItemDTO:
 class CartDTO:
     items: list[CartItemDTO]
     total: int
-    order_id: Optional[int] = None
+    order_id: int | None = None