Add and test xeus-r and xeus-python

[danielnachun]

I've recently become aware of some xeus kernels which may offer better performance than the original irkernel and ipython kernels because the backend is written in C++:

• xeus-r: https://github.com/jupyter-xeus/xeus-r
• xeus-python: https://github.com/jupyter-xeus/xeus-python

xeus-r currently has some blockers for R 4.4 support in conda-forge that need to be fixed, but I will test both kernels in a VM and on my Macbook to see how they behave in Jupyter and VSCode. If they are easy enough to set up, they may be good alternatives when working with large datasets.