0.6.2: Add LTAN and mean motion + Fix multithreading in python

New features and improvements

• feat: Add duration_to_radius function and utils, mean motion method to Orbit (mean_motion_deg_s), and Longitude of the Ascending Node (LTAN) (ltan_deg) by @ChristopherRabotin in #456
• a few typos and minor details by @fchapoton in #459

Bug Fixes

• Fix Python GIL deadlock in many functions by @ChristopherRabotin in #458

New Contributors

• @fchapoton made their first contribution in #459

Full Changelog: 0.6.1...0.6.2