Make set_node_child_without_hash return nothing

[Kevin Lewi]

Right now, when trying to migrate over state maps to use Storage, we are running into an issue that I think might be caused by this line:

https://github.com/novifinancial/SEEMless/blob/main/src/history_tree_node.rs#L173-L175

Here, we are potentially copying a child, implicitly cloning its state map. This gets problematic when we move to global storage. This could be solved by ensuring that set_node_child_without_hash doesn't return anything, and we find a better way to structure the code to achieve the same thing (without having to clone a child).