Add optical absorption model with imported data

[hhollenb]

The base optical Model class with AbsorptionModel as an example case. ImportedModels is a list of ImportOpticalModels with a map for built-in model classes to their imported identifier, and can be built directly or from imported data with a ModelImporter (included in a later PR). ImportedModelAdapter can then be used by models to access their MFP tables.

MFP tables are built with detail::MfpBuilder which internally handles the grid IDs that a model builds. It should probably be refactored when we refactor the rest of the grid builders.

For testing I created a MockImportData class to handle a bunch of common mock data and functions that the model classes use. I find that it makes writing the tests easy and fairly consistent, but could probably use a good critique.

[github-actions[bot]]

Test summary

 3 345 files   5 161 suites   3m 56s :stopwatch:  1 548 tests  1 520 :white_check_mark: 28 :zzz: 0 :x: 17 138 runs  17 075 :white_check_mark: 63 :zzz: 0 :x:

Results for commit f5d3329f.

:recycle: This comment has been updated with latest results.

[amandalund]

Sorry for the delay @hhollenb --this looks great at first glance, I'll go over it in detail first thing tomorrow!

[hhollenb]

Ack sorry I clicked merge before I read you comment. I'll setup the Rayleigh scattering PR which will be mostly the same and can be used for some further review.

[sethrj]

I didn't even realize you had permissions to merge 🤔