Use faster manual cast for fp8 in unet.

comfy/model_management.py

@@ -474,6 +474,20 @@ def unet_dtype(device=None, model_params=0):
         return torch.float16
     return torch.float32
 
+# None means no manual cast
+def unet_manual_cast(weight_dtype, inference_device):
+    if weight_dtype == torch.float32:
+        return None
+
+    fp16_supported = comfy.model_management.should_use_fp16(inference_device, prioritize_performance=False)
+    if fp16_supported and weight_dtype == torch.float16:
+        return None
+
+    if fp16_supported:
+        return torch.float16
+    else:
+        return torch.float32
+
 def text_encoder_offload_device():
     if args.gpu_only:
         return get_torch_device()
@@ -538,7 +552,7 @@ def get_autocast_device(dev):
 def supports_dtype(device, dtype): #TODO
     if dtype == torch.float32:
         return True
-    if torch.device("cpu") == device:
+    if is_device_cpu(device):
         return False
     if dtype == torch.float16:
         return True