Expose model params

[jvshields]

This PR restructures the high level run_stardis() function to only be a helper function that calls a couple other functions scattered throughout the code. This makes it much easier to effectively run the function on your own so you can parse a model, edit the model as a python object, and then run the rest of the function.

This is intended to make it easier to modify specific abundances and investigate their impacts on lines in the spectrum.

Still need to make an easy helper function that takes in the stellar model, and allows you to request an abundance of some given element, and then rescale the rest of the elements appropriately.

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 14 lines in your changes are missing coverage. Please review.

Project coverage is 68.20%. Comparing base (feeb2db) to head (0f6901b).

❗ Current head 0f6901b differs from pull request most recent head 60fdbc9. Consider uploading reports for the commit 60fdbc9 to get more accurate results

Files	Patch %	Lines
stardis/io/base.py	67.74%	10 Missing ⚠️
stardis/base.py	75.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #185      +/-   ##
==========================================
+ Coverage   67.91%   68.20%   +0.29%     
==========================================
  Files          31       32       +1     
  Lines        1203     1214      +11     
==========================================
+ Hits          817      828      +11     
  Misses        386      386              

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