Add ignored layers to FP8 Z-Image quality case

Signed-off-by: WeiQing Chen <david6666666@users.noreply.github.com>

tests/diffusion/quantization/artifacts/fp8_z_image_quality/README.md

@@ -10,6 +10,12 @@ VLLM_OMNI_QUALITY_OUTPUT_DIR=$PWD/tests/diffusion/quantization/artifacts/fp8_z_i
   -s -v -m ""
 ```
 
+Quantized config:
+
+```python
+{"method": "fp8", "ignored_layers": ["img_mlp"]}
+```
+
 Result: failed with the current `max_lpips=0.15` threshold.
 
 | Metric | Value |

tests/diffusion/quantization/test_quantization_quality.py

@@ -71,7 +71,7 @@ class QualityTestConfig:
     prompt: str  # generation prompt
     max_lpips: float  # fail threshold — higher = more lenient
     model: str | None = None  # HF model name
-    quantization: str | None = None  # quantization method, e.g. "fp8"
+    quantization: str | dict[str, object] | None = None  # quantization method/config, e.g. "fp8"
     baseline_model: str | None = None  # explicit BF16/local baseline path
     quantized_model: str | None = None  # explicit quantized/local model path
     height: int = 1024
@@ -118,7 +118,7 @@ QUALITY_CONFIGS = [
     QualityTestConfig(
         id="fp8_z_image",
         model="Tongyi-MAI/Z-Image-Turbo",
-        quantization="fp8",
+        quantization={"method": "fp8", "ignored_layers": ["img_mlp"]},
         task="t2i",
         prompt=(
             "A breathtaking twilight scene atop a floating archipelago of crystalline islands suspended in an "