[optimization] Added Wan 2.2 VAE decode optimizations (#7056)

Signed-off-by: Maciej Bala <mbala@nvidia.com>
Signed-off-by: MaciejBalaNV <mbala@nvidia.com>

tests/diffusion/test_diffusion_config_propagation.py

@@ -214,6 +214,17 @@ def test_qwen_image_edit_plus_sets_generic_multimodal_limit():
     assert od_config.max_multimodal_image_inputs == QWEN_IMAGE_EDIT_PLUS_MAX_INPUT_IMAGES
 
 
+def test_vae_fast_path_roundtrip():
+    assert _roundtrip_diffusion_config(model="x").vae_fast_path == "lossless"
+    od = _roundtrip_diffusion_config(model="x", vae_fast_path="channels_last")
+    assert od.vae_fast_path == "channels_last"
+
+
+def test_invalid_vae_fast_path_is_rejected():
+    with pytest.raises(ValueError, match="vae_fast_path"):
+        OmniDiffusionConfig(model="x", vae_fast_path="fast")
+
+
 def test_flux2_klein_sets_generic_multimodal_limit():
     od_config = OmniDiffusionConfig(
         model="black-forest-labs/FLUX.2-klein-9B",