Orbital elements based calculations

[attipaci]

Added

• NOVAS_ORBITAL_OBJECT to enum novas_planet.
• novas_orbital_elements structure, including novas_orbital_system substructure, and enum novas_reference_plane to distiguish ecliptic vs equatorial orbital parameters, and novas_set_orbital_pole() helper function to configure.
• object.orbit field containing novas_orbital_elements data
• novas_orbit_posvel() function to calculate position and velocity vectors from orbital elements.
• make_orbital_object() function to ease the creation of objects with orbital parameters.

Changed

• ephemeris() call to process NOVAS_ORBITAL_OBJECT types via novas_orbit_posvel().

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.70%. Comparing base (1e3d54e) to head (15911b9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #96      +/-   ##
==========================================
+ Coverage   99.65%   99.70%   +0.04%     
==========================================
  Files           8        8              
  Lines        2914     3024     +110     
  Branches      561      575      +14     
==========================================
+ Hits         2904     3015     +111     
+ Partials       10        9       -1     

Flag	Coverage Δ
unittests	99.70% <100.00%> (+0.04%)	⬆️

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Files with missing lines	Coverage Δ
src/frames.c	99.52% <ø> (ø)
src/novas.c	99.62% <100.00%> (+0.07%)	⬆️
src/super.c	100.00% <100.00%> (ø)

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