Make PPO loss hyper-parameters available to users

[BaohaoLiao]

Thnak you very much for this excellent work.

Here I want to ask whether it is possible to give us some choice to control the hyper-parameters of PPO loss, like clip_ratio_high and clip_rario_low, which is very important to control the exploration-exploitation of RL.

The Tinker documentation shows that we can implement the custom loss by ourselves. However, the tranining time will becomes x3, which is too much.

[Tiiiger]

Looking into it ...