feat: add Brouwer-Lyddane Mean Long and Mean Short elements

[vishwa2710]

• Have to add bindings, will do so after the C++ code is reviewed and any name/flow changes are addressed.
• Have to add docstrings to C++ code as well

[codecov]

Codecov Report

Merging #240 (51c8a07) into main (2200a55) will increase coverage by 0.11%.
The diff coverage is 84.55%.

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
+ Coverage   83.27%   83.39%   +0.11%     
==========================================
  Files          63       66       +3     
  Lines        4886     5505     +619     
==========================================
+ Hits         4069     4591     +522     
- Misses        817      914      +97     

Files	Coverage Δ
...els/BrouwerLyddaneMean/BrouwerLyddaneMeanShort.cpp	87.86% <87.86%> (ø)
...t/Models/BrouwerLyddaneMean/BrouwerLyddaneMean.cpp	80.17% <80.17%> (ø)
...dels/BrouwerLyddaneMean/BrouwerLyddaneMeanLong.cpp	90.51% <90.51%> (ø)
...trodynamics/Trajectory/Orbit/Models/Kepler/COE.cpp	79.31% <66.27%> (-3.92%)	⬇️

[Derollez]

Huge addition! Might want to add validation tests against GMAT or Orekit? (at least one set of propagated and computed BL values to ensure this is good?)

[vishwa2710]

Amazing thank you for the feedback. All the unit tests are compared to GMAT so I will put that in the comments.

[kyle-cochran]

Some suggestions to simplify RuntimeError printing.

Will do another, less superficial, review round

[kyle-cochran]

A lot of nit suggestions on adding const-ness to the return types for the getters of the more trivial types (Angle/Length/etc)