[Quantization] Migrate GGUF diffusion model support to OOT plugin (#4769)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>
Signed-off-by: Isotr0py <Isotr0py@outlook.com>

tests/entrypoints/test_async_omni_diffusion_config.py

@@ -359,3 +359,15 @@ def test_resolve_stage_configs_injects_additional_config_into_diffusion_stage(mo
 
     assert not hasattr(stage_configs[0].engine_args, "additional_config")
     assert stage_configs[1].engine_args.additional_config == {"torchair_graph_config": {"enabled": True}}
+
+
+def test_default_stage_config_includes_quantization_config():
+    """Ensure structured quantization_config survives default diffusion-stage creation."""
+    quantization_config = {
+        "method": "example_quant",
+        "weights": "weights.bin",
+    }
+
+    stage_cfg = AsyncOmniEngine._create_default_diffusion_stage_cfg({"quantization_config": quantization_config})[0]
+
+    assert stage_cfg["engine_args"]["quantization_config"] == quantization_config