translate spinup stability script to python

There are some existing ncl scripts for assessing spinup stability in tools/contrib. There are a view key reasons that it might be nice to have this available as a python tool.

1. deprecation of ncl
2. python (dask) would allow parallelization which would make processing monthly data faster
3. we can use yaml files to configure stability thresholds without editing the script
4. I've found with python I can easily parse the stability status for automated spinup workflows

I have an existing script for this that I'll put in a PR, but it's probably still missing a couple of things that could be beneficial (e.g. unstructured grids)