* [Enhance] Imporve efficiency of precision, recall, f1_score and support.
* Fix bugs
* Use np.maximum since torch doesn't have maximum before torch 1.7
* Fix bug
* Refactor unit tests folder structure.
* Remove label smooth and Vit test in `test_classifiers.py`
* Rename test_utils in dataset to test_dataset_utils
* Split test_models/test_utils/test_utils.py to multiple sub files.
* Add unit tests of classifiers and heads
* Use patch context manager.
* Add unit test of `is_tracing`, and add warning in `is_tracing` if torch
verison is smaller than 1.6.0