Add a --bf16-unet to test running the unet in bf16.

comfy/model_management.py

@@ -449,6 +449,8 @@ def unet_inital_load_device(parameters, dtype):
         return cpu_dev
 
 def unet_dtype(device=None, model_params=0):
+    if args.bf16_unet:
+        return torch.bfloat16
     if should_use_fp16(device=device, model_params=model_params):
         return torch.float16
     return torch.float32