Use the lastest version of gsplat cuda backend

[zhiguotang5]

I notice your repo use the gsplat which is from the old version of cuda backend. The newest version of gsplat have many good features such as mip-splatting, and memory efficient, would you update your gsplat cuda backend to the latest version of gsplat cuda backend?

[pierotofy]

We'd welcome a PR to bring any new features / enhancements from upstream.