Improve OrbitalData inference

[charleskawczynski]

This PR adds some type assertions to fix some JET failures (from 145 -> 73). The remaining ones are in DelimitedFiles and Interpolations.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.94%. Comparing base (cc49082) to head (43349c3).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
+ Coverage   98.93%   98.94%   +0.01%     
==========================================
  Files           4        4              
  Lines          94       95       +1     
==========================================
+ Hits           93       94       +1     
  Misses          1        1              

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[Sbozzolo]

This change slightly modifies the function:

• now x[1, 1] and x[end, 1] have to be integer
• the independent variable in the spline is now defined in terms of integers instead of floats

But I don't see any problems with these, so I'd say that we can go ahead with the change.

Maybe we can add one line of comment to mention that this code looks a little funky to ensure type stability. (And format before merging)

[charleskawczynski]

I was able to remove the Int conversion while still fixing inference failures, it was just the readdlm that was type-unstable.