Explore adding pyspedas interface to spacepy IRBEM implementation.

[jameswilburlewis]

spacepy apparently includes support for several field models, including some of the Tsyganenko models, under its IRBEMPY module:

https://spacepy.github.io/autosummary/spacepy.irbempy.get_Bfield.html#spacepy.irbempy.get_Bfield

It sounds like these are compiled Fortran libraries, so they might be a lot more efficient than geopack, at least for the models supported by IRBEM. We would need to vet them against the IDL geopack results, of course...