Add implementations of KDTree / BallTree

Hello,

thanks for exposing and maintaining this library of Numba examples.

I have a full-Numba implementation of both KDTrees and BallTrees, and wondered whether this would be valuable to add in this repo.
My code is [here](https://github.com/remydubois/lsnms/blob/main/lsnms/kdtree.py), and I am willing to enrich it (add a few extra necessary methods) in order to match the minimal functionalities required by most use cases / or match the implementations standards that may reign in this repo.

Let me know,

Start by reading the proposed implementation in lsnms/kdtree.py and comparing it with the existing examples in this repository. Determine which KDTree and BallTree methods and repository standards are required; the work is done when the implementations provide the agreed minimal functionality and fit the project's example structure.

Written by the indexing model from the issue text.