fix: Import date type explicitly to fix isinstance checks

When we import datetime from the datetime module, we get the datetime class,
not the module. This caused isinstance() checks to fail when checking against
datetime.date (which doesn't exist when datetime is a class).

Solution: Import date explicitly from datetime module and use it in isinstance
checks. Order matters - check datetime before date since datetime is a subclass
of date.

Fixes: "isinstance() arg 2 must be a type, a tuple of types, or a union"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/transformers/data_transformer.py

@@ -1,6 +1,6 @@
 """Data transformation from MySQL to PostgreSQL format."""
 from typing import Dict, Any, List, Tuple
-from datetime import datetime, time, timedelta
+from datetime import datetime, time, timedelta, date
 from config import (
     RAWDATACOR_COLUMNS,
     ELABDATADISP_FIELD_MAPPING,
@@ -15,25 +15,25 @@ class DataTransformer:
     """Transform MySQL data to PostgreSQL format."""
 
     @staticmethod
-    def _convert_date(event_date: Any) -> datetime.date:
-        """Convert event_date to datetime.date object.
+    def _convert_date(event_date: Any) -> date:
+        """Convert event_date to date object.
 
         Handles multiple input types:
         - str: Parse from "YYYY-MM-DD" format
-        - datetime.date: Return as-is
-        - datetime.datetime: Extract date component
+        - date: Return as-is
+        - datetime: Extract date component
 
         Args:
             event_date: Date value from MySQL (str or date)
 
         Returns:
-            datetime.date object
+            date object
         """
         if isinstance(event_date, str):
             return datetime.strptime(event_date, "%Y-%m-%d").date()
         elif isinstance(event_date, datetime):
             return event_date.date()
-        elif isinstance(event_date, datetime.date):
+        elif isinstance(event_date, date):
             return event_date
         else:
             raise ValueError(f"Unsupported event_date type: {type(event_date)}")