Add reader and fit function for longitudinal files

[maxnoe]

No description provided.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (bdf5174) 95.48% compared to head (8ade117) 95.46%.

Files	Patch %	Lines
corsikaio/longitudinal.py	91.83%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #39      +/-   ##
==========================================
- Coverage   95.48%   95.46%   -0.03%     
==========================================
  Files          20       22       +2     
  Lines         643      727      +84     
==========================================
+ Hits          614      694      +80     
- Misses         29       33       +4     

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[orelgueta]

All good, but you are missing tests for all the cases in which the input file is wrong (all the ValueErrors raised). Not a big deal, so I approve already.

[maxnoe]

Yes, the unhappy paths are a bit hard to test in a meaningful way, since I have not yet encountered any broken longitudinal files.

I can test using some dummy data, but for any meaningful error handling, we need to have people report real-world issues and then add tests for that.