feat: add UserId value object and update ClassifiedAd to use it

domain/marketplace/classified_ad.py

@@ -2,11 +2,13 @@ from dataclasses import dataclass
 from decimal import Decimal
 from uuid import UUID
 
+from domain.marketplace.user_id import UserId
+
 
 @dataclass(frozen=True)
 class ClassifiedAd:
     id: UUID
-    _ownerId: UUID
+    _ownerId: UserId
     title: str
     text: str
-    _price: Decimal
+    _price: Decimal