feat: add Money value object

tests/test_money.py

@@ -0,0 +1,24 @@
+from decimal import Decimal
+
+from domain.marketplace.money import Money
+
+
+def test_money_creation():
+    money = Money(amount=Decimal("99.99"))
+    assert money.amount == Decimal("99.99")
+
+
+def test_money_is_immutable():
+    money = Money(amount=Decimal("10.00"))
+
+    try:
+        money.amount = Decimal("20.00")  # type: ignore
+        assert False, "Should have raised FrozenInstanceError"
+    except AttributeError:
+        pass
+
+
+def test_money_equality():
+    money1 = Money(amount=Decimal("50.00"))
+    money2 = Money(amount=Decimal("50.00"))
+    assert money1 == money2