Fix spherical to Cartesian conversion in State.from_ephem

[mkelley]

Fixes #450 .

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.11%. Comparing base (e720e46) to head (17e9e3d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #452   +/-   ##
=======================================
  Coverage   82.11%   82.11%           
=======================================
  Files          53       53           
  Lines        4339     4339           
=======================================
  Hits         3563     3563           
  Misses        776      776           

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