SIENTIAPDE-1646 Refactor MLFlow tests and update artifact handling
- Enhanced test cases for MLFlow to improve clarity and accuracy in data handling.
- Updated references in tests to use 'evaluation_data.csv' and 'test_data.csv' instead of 'retrain_input.csv' and 'train_data.csv'.
- Introduced a new helper function for creating prediction frames to streamline test setup.
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