feat: add ClassifiedAdText value object and use it in ClassifiedAd

tests/test_classified_ad_text.py

@@ -0,0 +1,7 @@
+from domain.marketplace.classified_ad_text import ClassifiedAdText
+
+
+def test_classified_ad_text_creation():
+    text = ClassifiedAdText(text="This is a classified ad description.")
+
+    assert text.text == "This is a classified ad description."