mix of dir and files allowed. this ref #294

[JeanBilheux]

I added the possibility to define the CT as a folder and the rest as a list of files

[codecov]

Codecov Report

Attention: Patch coverage is 78.94737% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 94.58%. Comparing base (bfc0433) to head (15a100d).
Report is 2 commits behind head on next.

Files	Patch %	Lines
src/imars3d/backend/dataio/data.py	78.94%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #296      +/-   ##
==========================================
- Coverage   94.83%   94.58%   -0.26%     
==========================================
  Files          21       21              
  Lines        1239     1255      +16     
==========================================
+ Hits         1175     1187      +12     
- Misses         64       68       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[KedoKudo]

There are a lot of unrelated files added to this PR. Could you clean them up? Also, it would be great if you could add some unit test for the new signature (if you are using vscode+copilot, you can ask copilot to generate the unit test for you).