1. why apply projector before calc bt_loss?  https://github.com/THUDM/RecDCL/blob/60d3155ff630472765ff0fde1faead960b1ac238/recbole/model/general_recommender/recdcl.py#L121C1-L130C18 3. why not apply l2_norm when predict?  https://github.com/THUDM/RecDCL/blob/60d3155ff630472765ff0fde1faead960b1ac238/recbole/model/general_recommender/recdcl.py#L167C4-L172C52