Remaining Problems Regarding Training metric

[zhaochenyang20]

@Eren Chenyang Zhao 赵晨阳, of course, you can use on_epoch_end, but I had a few concerns at that time. (1) What should I do if I want the eval_strategy to be "steps"? (2) How does this support the trainer's built-in selection of the best metrics? You only performed the evaluation and printed the results.