SIENTIAPDE-1325

Enhance metrics handling in Gates and MLFlow classes

- Added checks for `None` response times before emitting OPC writing metrics in the Gates class to prevent unnecessary metric emissions.
- Updated the MLFlow class to conditionally sort and drop duplicates based on the presence of the 'created_at' column, ensuring robustness in data processing.
- Adjusted corresponding tests to validate the new behavior in both classes.

tests/laborious/activities/test_mlflow.py

@@ -254,11 +254,11 @@ async def test_retrain_model_success_data_success_retrain(mock_to_datetime, mlfl
 
     timestamp = raw_data.__getitem__.return_value.max.return_value
 
-    raw_data.sort_values.assert_called_once_with('created_at', ascending=False)
-    raw_data.sort_values.return_value.drop_duplicates.assert_called_once_with(
+    raw_data.sort_values.assert_not_called()
+    raw_data.drop_duplicates.assert_called_once_with(
         subset=['variable', 'timestamp'], keep='first'
     )
-    raw_data = raw_data.sort_values.return_value.drop_duplicates.return_value
+    raw_data = raw_data.drop_duplicates.return_value
 
     raw_data.drop.assert_has_calls(
         [
@@ -313,7 +313,9 @@ async def test_retrain_model_success_data_fail_retrain(mock_to_datetime, mlflow)
         'message': 'Model retrained failed.',
     }
 
-    mlflow.minio_repository.get_parquet_as_dataframe.return_value = MagicMock()
+    mlflow.minio_repository.get_parquet_as_dataframe.return_value = MagicMock(
+        columns=['variable', 'timestamp', 'value', 'created_at']
+    )
 
     response = await mlflow.retrain_model(
         {