Igrf

Use Matlab test unit class

Attempt to make CMake build more robust from Python

Thanks to rprechelt and stopyun-jirong who noted the new syntax of xarray made this IGRF Python interface need updating

Updated annotation to Python 3.10 style (backward compatible to Python 3.7)

Removed unnecessary CMake code

Update to use IGRF13 model

* use CLI interface instead of f2py--solves numerous long-standing issues in general with f2py by not using it
* use Python >= 3.7 for reliability across Python install types
* add CI to CLI as well as module
* update Matlab interface

* apply project template
* add initial geomag7.0 C code
* vendor datetime2yeardec

modularize for best practice

add examples