Use faster manual cast for fp8 in unet.

comfy/supported_models_base.py

@@ -22,6 +22,8 @@ class BASE:
     sampling_settings = {}
     latent_format = latent_formats.LatentFormat
 
+    manual_cast_dtype = None
+
     @classmethod
     def matches(s, unet_config):
         for k in s.unet_config:
@@ -71,3 +73,5 @@ class BASE:
         replace_prefix = {"": "first_stage_model."}
         return utils.state_dict_prefix_replace(state_dict, replace_prefix)
 
+    def set_manual_cast(self, manual_cast_dtype):
+        self.manual_cast_dtype = manual_cast_dtype