SphericalCoordinates: make query methods const

[adityapande-1995]

Signed-off-by: Aditya aditya050995@gmail.com

🦟 Bug fix

Summary

This PR changes SurfaceRadius, AxisEquatorial, AxisPolar, Flattening methods to const, similar to other existing methods Heading(), LatitudeReference(), etc.

Also adds comments to exclude deprecated distance function from code coverage.

Follow up to #434

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

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[codecov]

Codecov Report

Merging #452 (bb46c61) into main (33a4827) will increase coverage by 0.03%.
The diff coverage is 100.00%.

❗ Current head bb46c61 differs from pull request most recent head f940826. Consider uploading reports for the commit f940826 to get more accurate results

@@            Coverage Diff             @@
##             main     #452      +/-   ##
==========================================
+ Coverage   99.65%   99.68%   +0.03%     
==========================================
  Files          73       73              
  Lines        6641     6639       -2     
==========================================
  Hits         6618     6618              
+ Misses         23       21       -2     

Impacted Files	Coverage Δ
src/SphericalCoordinates.cc	99.68% <100.00%> (+0.63%)	⬆️

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