Addition of Brown Dwarves into SPISEA

[caitlinbegbie]

This pull request incorporates all of the changes I have made to incorporate brown dwarf stars and their properties as both primary masses and companions. The main changes are as follows:

1. Expansion of lower masses available to be generated.
2. Creation of new IMF, Salpeter_Kirkpatrick_2024, to model accurate BD generation.
3. Addition of new evolution model, MergedPhillipsBaraffePisaEkstromParsec to include solar metallicity BDs from logages of ~6-10. Interpolation methods to merge models together where no data is present, and new flag in the stars and companions tables to inform a user of an object is in an interpolated region.
4. Creation of a new compact remnant phase (phase=90) to classify BDs specifically and bring them into clusters with and without multiplicity.
5. Addition of Meisner and Phillips atmospheric grids for brown dwarfs, and updated merged model and grids.
6. Updated multiplicity and resolved cluster statistics for brown dwarfs.
7. Updated testing for all changes.

An outline of clusters generated with brown dwarf masses can be found in the notebook SPISEA/changes/BD_Clusters.ipynb.