feat: add the example script of colossus (#558)

* add colossus script

* finalize colossus

examples/flux.1-dev-colossus.py

+import torch
+from diffusers import FluxPipeline
+
+from nunchaku import NunchakuFluxTransformer2dModel
+from nunchaku.utils import get_precision
+
+precision = get_precision()  # auto-detect your precision is 'int4' or 'fp4' based on your GPU
+transformer = NunchakuFluxTransformer2dModel.from_pretrained(
+    f"nunchaku-tech/nunchaku-flux.1-dev-colossus/svdq-{precision}_r32-flux.1-dev-colossusv12.safetensors"
+)
+pipeline = FluxPipeline.from_pretrained(
+    "black-forest-labs/FLUX.1-dev", transformer=transformer, torch_dtype=torch.bfloat16
+).to("cuda")
+image = pipeline(
+    "face portrait of a 20 years old woman , gothic short blue hair, ruby collar, she is touch her cheek",
+    num_inference_steps=50,
+    guidance_scale=3.5,
+).images[0]
+image.save(f"flux.1-dev-colossus-{precision}.png")