feat: enhance E2E testing setup and model reporting

- Added a new fixture to manage runtime report artifacts in a writable temp directory during E2E tests, addressing permission issues in local CI/dev environments.
- Updated `conftest.py` to include a requirements.txt file in the model packaging path for training activities.
- Refactored existing fixtures to use `pytest.fixture` instead of `pytest_asyncio.fixture` for better compatibility.
- Enhanced the `Reports` class to include a target alias for report metrics, ensuring compatibility with Evidently's reporting requirements.
- Introduced new test scenarios to validate the handling of missing and whitespace-only `date_column` inputs in the training workflow.

These changes improve the robustness of the E2E testing framework and enhance the clarity of model reporting metrics.

tests/activities/test_training.py

@@ -131,13 +131,15 @@ def test_train_model_success_serializes_result(mock_mlflow, training):
 
     training.minio_repository.download_file = MagicMock(return_value=b'csv')
     training.data_manager_repository.prepare_training_data = MagicMock(return_value=tmr)
+
+    def _set_metrics(x, _w, **_kw):
+        x.mse_val = 0.1
+        x.mae_val = 0.2
+        x.r2_val = 0.9
+        return x
+
     training.data_manager_repository.compute_regression_metrics = MagicMock(
-        side_effect=lambda x, _w, **_kw: (
-            setattr(x, 'mse_val', 0.1),
-            setattr(x, 'mae_val', 0.2),
-            setattr(x, 'r2_val', 0.9),
-            x,
-        )[-1]
+        side_effect=_set_metrics
     )
 
     def _fill_report(x, **_kw):