Extend OrbitElements Class with New Methods and Add Pytest Coverage

[JaskRendix]

PR improves the OrbitElements class by adding several new methods and properties to make it more functional and easier to use. It also introduces a full pytest test suite to verify the correctness of the class (before and after) and its behavior under different conditions.

The changes include:

• new properties: apogee, is_circular, and is_retrograde
• new methods: position_vector(), velocity_at_perigee(), velocity_at_apogee() and to_tle_dict()
• a set of unit tests using pytest to cover both the original and new functionality

These additions were made as part of a satellite tracking project where I needed access to derived orbital parameters and a reliable way to validate them. The test suite ensures the class behaves correctly and can be extended in future work.

• Tests added
• Fully documented

[djhoese]

Thanks! This looks pretty good. I have one important question and one small request.

[codecov]

Codecov Report

❌ Patch coverage is 99.53917% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.43%. Comparing base (c9e2909) to head (b10cfeb).
⚠️ Report is 50 commits behind head on main.

Files with missing lines	Patch %	Lines
pyorbital/tlefile.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #204      +/-   ##
==========================================
+ Coverage   89.78%   90.43%   +0.65%     
==========================================
  Files          17       18       +1     
  Lines        2809     3011     +202     
==========================================
+ Hits         2522     2723     +201     
- Misses        287      288       +1     

Flag	Coverage Δ
unittests	90.43% <99.53%> (+0.65%)	⬆️

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[coveralls]

coverage: 90.396% (+0.7%) from 89.742%
when pulling b10cfeb on JaskRendix:orbit-elements
into ce9856a on pytroll:main.

[djhoese]

👀 oh I like the 0.8% increase in test coverage. Nice.

[djhoese]

A couple more requests for the test code. Thanks again for working on this.

[djhoese]

CI is running at I type this so if they fail you may need to give some of the equality checks a little less precision. Otherwise, looks good to me! Thanks.

@mraspaud @adybbroe @pnuu any other opinions? I definitely shouldn't be the primary voice of approval/reason here.

[pnuu]

Thank you for the new features and the bug fix!

I've added one refactoring suggestion, but I'm not sure it really helps the code 😅

[mraspaud]

Thanks a lot for your contribution! I'm really grateful for the nice cleanups and refactors along with a bug fix on top of the added functionality.
I have a minor improvement suggestion inline, but this looks ready otherwise I think.

[mraspaud]

LGTM, thanks a lot for taking the time to improve pyorbital!