fix on datetime serialization

JobDescription.py

@@ -19,7 +19,7 @@ class JobDescription:
             "company": self.company,
             "url": self.url,
             "company_url": self.company_url,
-            "published_at": self.published_at,
+            "published_at": self.published_at.isoformat() if self.published_at else None,
             "job_description": self.job_description,
             "organization_logo_url": self.organization_logo_url,
             "ai_result": self.ai_result.to_dict() if self.ai_result else None,
@@ -29,23 +29,18 @@ class JobDescription:
     @staticmethod
     def from_dict(data):
         ai_result = AIInformation.from_dict(data["ai_result"]) if data["ai_result"] else None
-        return JobDescription(
+        job_desc = JobDescription(
             title=data["title"],
             company=data["company"],
             url=data["url"],
             company_url=data["company_url"],
             job_description=data["job_description"]
-        )._replace(
-            published_at=data["published_at"],
-            organization_logo_url=data["organization_logo_url"],
-            ai_result=ai_result,
-            salary_range=data["salary_range"]
         )
-
-    def _replace(self, **kwargs):
-        for key, value in kwargs.items():
-            setattr(self, key, value)
-        return self
+        job_desc.published_at = datetime.fromisoformat(data["published_at"]) if data["published_at"] else None
+        job_desc.organization_logo_url = data["organization_logo_url"]
+        job_desc.ai_result = ai_result
+        job_desc.salary_range = data["salary_range"]
+        return job_desc
     
     def format_should_apply(self, should_apply : bool):
         if should_apply: