Sun observer angle calculation (or solar probe angle)

[ChristopherRabotin]

Summary

New feature: computation of the sun angle between an observer (e.g. a probe) and another celestial object (e.g. the primary body that probe orbits). This allows the computation of the Sun-probe-Earth angle, for example, if the observer is the probe and the target is the primary body it orbits.

Architectural Changes

No change

New Features

• Add sun_angle_deg and sun_angle_deg_from_frames function signatures

Improvements

No change

Bug Fixes

No change

Testing and validation

• Test that with the gmat-hermite.bsp file, which contains ~ 3 hours of Earth centered propagation, the computation of the SPE is (almost) exactly 90 degrees greater than the Sun elevation at the point exactly nadir of the spacecraft at a geodetic height of zero kilometers. An error of 0.05 degrees is acceptable because the SPE does not account for the flattening of the Earth but the elevation does since it's computed from the latitude and longitude in the IAU Earth frame, which accounts for that flattening ratio.

Documentation

This PR does not primarily deal with documentation changes.

[codecov]

Codecov Report

Attention: 21 lines in your changes are missing coverage. Please review.

Comparison is base (f413f5f) 79.68% compared to head (5591b2c) 80.14%.

Files	Patch %	Lines
anise/src/almanac/bpc.rs	38.70%	19 Missing ⚠️
anise/src/naif/spk/summary.rs	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
+ Coverage   79.68%   80.14%   +0.46%     
==========================================
  Files          70       71       +1     
  Lines        8506     8653     +147     
==========================================
+ Hits         6778     6935     +157     
+ Misses       1728     1718      -10     

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