neurodata/scikit-learn#54 will introduce the partial_fit api for classification trees

I just reviewed the code, and I think we need to update Cython code based on the _set_split_node API being overridden already within _oblique_tree: https://github.com/neurodata/scikit-tree/blob/b44c9518057f44060cfc8cc0d08148de87685ce3/sktree/tree/_oblique_tree.pyx#L232-L239.

Rn _set_split_node assumes the node_id is self.node_count. Perhaps we should refactor sklearn _set_split_node to get passed in the node_id and make relevant changes here in _oblique_tree? That way neurodata/scikit-learn#54 should work out of the box for oblique tree classifiers.

cc: @PSSF23 do you want to handle this refactoring inside your current partial_fit PR?