Add Krea 2 (K2) text-to-image pipeline and transformer (#14045)
Adds Krea2Transformer2DModel and Krea2Pipeline: a flow-matching
text-to-image MMDiT with grouped-query attention, Qwen3-VL text
conditioning, and the Qwen-Image VAE.
Co-authored-by: Elea Zhong <elea@krea.ai>
Co-authored-by: Naga Sai Abhinay Devarinti <devarintinagasaiabhinay@gmail.com>