[Refactor] Refactor `after_val_epoch` to make it output metric by epoch (#278)

* [Refactor]:Refactor `after_val_epoch` to make it output metric by epoch

* add an option for user to choose the way of outputing metric

* rename variable

* reformat docstring

* add type alias

* reformat code

* add test function

* add comment and test code

* add comment and test code