Add stable diffusion 3 / MMDiT based model support

[isidentical]

trafficstars

SD3 is coming up and it's architecture is already public / described in paper. I think it can be supported even before the weights drop or at least the initial work can be started. Here is an example MMDiT implementation by @kabachuha https://github.com/NUS-HPC-AI-Lab/OpenDiT/pull/92

[ltdrdata]

Comfy implemented SD3 support, already. Just it seems that comfy is waiting the release.

[isidentical]

Is there a branch already?

[mcandre]

Several weeks have passed. Which milestone will include SD3 support?

[mcmonkey4eva]

Support for SD3 in Comfy will be released on the day SD3 itself is released, ie June 12th