[TODO] perform node regularization right after the node is generated for multi-evaluation tree

[hwpang]

No description provided.

[hwpang]

I don't remember what this issue is about lol, @mjohnson541 do you remember? If not I will close this for now.

[mjohnson541]

So I think this is about when we regularize nodes during training, whether it is done when we generate the node or as post-processing. I don't distinctly recall why this was important, but it should be straightforward.