Consider reintroducing color BC table options

I've received comments from some users who have been reading in their own BC tables in r24.08.1 and prior. There is some frustration over BC tables options being removed from MESA during the colors overhaul.

An example inlist from a user has something like:

! Extra color files
color_num_files=3
color_file_names(2)='blackbody_johnson.dat'
color_num_colors(2)=5
color_file_names(3)='extras/extra_color_file.dat'
color_num_colors(3)=17

In this circumstance, the user was reading in ecternal BC tables, for example the mist tables, since they cover a wider range than the Atlas9 models in some regions. It seems, providing users with both the old BC table controls as an option along with the new atm convolution approach would be the best approach.

Perhaps we can reintroduce these controls from the old colors module, so it is backwards compatible with some of the features present before the colors module rehaul.

@nialljmiller, do you know how much work would be involved in carrying this out? I'm not suggesting you do this. it is certainly something I or someone else could address in the future.

Start by comparing the old colors module's color_num_files, color_file_names, and color_num_colors controls with the current atm convolution approach. Use the example inlist and external BC tables described in the issue to define compatibility; done means users can select those legacy BC tables while the new approach remains available.

Written by the indexing model from the issue text.