diffusers safetensors stable-diffusion stable-diffusion-diffusers text-to-image full pixart pixart sigma base_model:PixArt-alpha/PixArt-Sigma-XL-2-1024-MS base_model:finetune:PixArt-alpha/PixArt-Sigma-XL-2-1024-MS license:creativeml-openrail-m diffusers:PixArtSigmaPipeline region:us