added custom serializer for dates, as pymongo cannot handle them

src/fiber_package/entity/person.py

@@ -1,4 +1,4 @@
-from pydantic import model_validator, EmailStr, Field, computed_field
+from pydantic import model_validator, EmailStr, Field, computed_field, field_serializer
 from typing import Self, Literal
 from datetime import date
 
@@ -44,3 +44,7 @@ class PersonModel(FiberBaseModel):
         full_name += " " + self.last_name
         self.full_name = full_name
         return self
+
+    @field_serializer("date_of_birth", when_used="always")
+    def serialize_date(self, value: date | None):
+        return value.isoformat() if value else None