[REQ] FxSR support

[FxSR](https://github.com/seungho-snu/FxSR)

While I can load the model with VSGAN, I can't change [the "t" value for potentially better results.](https://github.com/seungho-snu/FxSR/blob/main/figure/FxSR-PD_4x.png)

Thanks!