Accept documented groundTrack input forms

[sylvesterkaczmarek]

Summary

groundTrack() documents support for array_like positions and for a list of Orbit objects, but both forms currently fail before propagation: Python position lists reach _countR() without conversion to an ndarray, while lists of scalar orbits are misclassified as raw positions.

Normalize position inputs in _countR(), including a single three-vector, and route non-empty lists or tuples of Orbit objects through the existing _countOrbit() path. The existing deprecation warning for list-of-Orbit syntax is preserved.

Validation

Python 3.12 on macOS arm64:

• New regressions on unchanged main (45730dc): 3 failed. After the fix: all 3 passed.
• Focused compute suite: 20 passed.
• Full suite: 337 passed, 2 skipped, 35 subtests passed.
• py_compile and git diff --check passed.
• Flake8 reports no new findings in the changed code; the pre-existing findings in compute.py and test_compute.py remain unchanged.

No propagator or coordinate-frame behavior changes for existing ndarray and Orbit inputs.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.39%. Comparing base (45730dc) to head (c5a8105).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #148   +/-   ##
=======================================
  Coverage   97.39%   97.39%           
=======================================
  Files          17       17           
  Lines        5897     5902    +5     
=======================================
+ Hits         5743     5748    +5     
  Misses        154      154           

Flag	Coverage Δ
unittests	97.39% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
ssapy/compute.py	94.99% <100.00%> (+0.06%)	⬆️

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[sylvesterkaczmarek]

This has been open for about 11 days with no maintainer feedback. The branch is current, mergeable, and all current checks are green. Could a maintainer review it when convenient?