create masking/cropping library so it can be used by most (python plugins)

It would be interesting to create a library out of this file to allow for general purpose masking, cropping, regridding.

• afaik it works for regular, gaussian, curvilinear, rotated grids
• it preserves all ancillary variables (such as bnds) after the masking is done.

TODO:

• refactor (make a class? add more options?)
• more shapefiles?
• pytest
• documentation

roadmap by chatgpt