skip init for speed up z image constructor (#228)

* skip init for speed up z image constructor

* up

* up

Author: qzzz95

diffsynth_engine/models/z_image/qwen3.py

@@ -59,8 +59,11 @@ def from_state_dict(
         device: str = "cuda:0",
         dtype: torch.dtype = torch.bfloat16,
     ):
-        model = cls(config=config, device="meta", dtype=dtype)
+        with torch.device("meta"):
+            model = cls(config=config, device="meta", dtype=dtype)
         model.requires_grad_(False)
+
+        model.rotary_emb = Qwen3RotaryEmbedding(config=config, device=device)
         model.load_state_dict(state_dict, assign=True)
         model.to(device=device, dtype=dtype, non_blocking=True)
         return model

diffsynth_engine/models/z_image/z_image_dit.py

@@ -584,7 +584,8 @@ def from_state_dict(
         dtype: torch.dtype,
         **kwargs,
     ):
-        model = cls(device="meta", dtype=dtype, **kwargs)
+        with torch.device("meta"):
+            model = cls(device="meta", dtype=dtype, **kwargs)
         model = model.requires_grad_(False)
         model.load_state_dict(state_dict, assign=True)
         model.to(device=device, dtype=dtype, non_blocking=True)