Splatfacto with batch training

[hardikdava]

Great work of Nerfstudio. I have been using it daily. Current version of splatfacto does not have batch training option. Since gsplat supports batch training with multiple camera together. I am requesting to support for batch training for splatfacto. I think it will impact huge in terms of speed and gets training much faster and it will utilize full usage of GPU. I am willing to implement with guidance from maintainers.

[akristoffersen]

#3582 here is a WIP for this.