Save ParaStell Class Objects

[connoramoreno]

It could be nice to provide the option to save ParaStell class objects (i.e., Stellarator, InVesselBuild, MagnetSet, and SourceMesh) to a file that can later be loaded into a separate script. This way, users could reference useful data we store, such as volume IDs, source mesh strengths, etc. This may be possible via the pickle module (see this example).

[Edgar-21]

I've had issues with pickle and netCDF4 objects in the past - some of the multithreading approaches I tried for the nwl used pickle to pass off copies to each thread and that failed, but not sure if that is specific to how the that multithreading module uses it or is just an issue with netCDF4 objects in general.