Add vald to atom data

[jvshields]

:pencil: Description

Type: | :rocket: feature | :roller_coaster: infrastructure

This PR adds various helper functions to the vald reader to remove molecules from the linelist files, and then create a linelist with only the necessary columns for future use.

Also adds the vald_reader as an optional parameter for the TARDISAtomData class.

This is built on top of pr #379 and should not be merged before that one.

:vertical_traffic_light: Testing

How did you test these changes?

• [x] Testing pipeline
• [ ] Other method (describe)
• [ ] My changes can't be tested (explain why)

:ballot_box_with_check: Checklist

• [x] I requested two reviewers for this pull request
• [ ] I updated the documentation according to my changes
• [ ] I built the documentation by applying the build_docs label

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[codecov[bot]]

Codecov Report

Merging #380 (215e301) into master (c43d1f2) will increase coverage by 0.13%. The diff coverage is 13.24%.

@@            Coverage Diff             @@
##           master     #380      +/-   ##
==========================================
+ Coverage   68.40%   68.54%   +0.13%     
==========================================
  Files          30       30              
  Lines        3586     3608      +22     
==========================================
+ Hits         2453     2473      +20     
- Misses       1133     1135       +2     

Files	Coverage Δ
carsus/io/vald/vald.py	95.08% <100.00%> (+4.60%)	:arrow_up:
carsus/io/output/base.py	8.90% <2.06%> (-0.07%)	:arrow_down:

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[andrewfullard]

Looks like we need a test for strip_molecules=True according to codecov