Add Flux.2 Klein Inpaint pipeline

[Natans8]

The currently implemented Flux2KleinPipeline supports txt2img and img2img, however there isn't an option to pass a mask image to it.

A Flux2KleinInpaintPipeline would be most useful to address this case and allow to use the model to its full extent.

[ansonphong]

Yes having masked inpainting is critical for my application. There is no way to implement Flux2 in my app without this feature. Please add it, thanks!

[adi776borate]

Hi! I’d like to take this up.
I’ve reviewed the Flux.2 Klein pipeline and have started drafting the inpainting pipeline. For implementation details, I’ll be using FluxInpaintPipeline as my primary reference.