[FR] Support for attention masking

[asagi4]

I really want to be able to use attention masking instead of ComfyUI's current whatever it's doing.

The existing implementations don't work with scheduled conds and seem difficult to adapt. IPAdapterPlus seems to have a good approach, but it's specialized for IPA conds so I can't quite steal it as is.

[asagi4]

There's a test implementation of an attention mask hook using the patch_hooks2 pull request.

It seems to work, but is kind of slow. I'm not sure if the slowness is just a result of the masking, or if it's because ComfyUI isn't able to batch conds.