Lunarsky

Added
- Support for ellipsoid models for selenodetic coordinates (non-spherical)

Deprecated
- Removed support for Python < 3.9. Astropy >= 6.0 is required for ellipsoid support

Fixed
- Updated version of pre-commit-hooks used
- Accept tuple for location in Time class (in this case, assumes EarthLocation)
- Use newer PCK file in unit test with Earth positioning.
- Match behavior of astropy when transforming non-unit cartesian positions without units (treat as unitspherical using direction info only)
- Now tracking available lunar station_ids, instead of incrementing a counter naively.

Deprecated
- Dropping support for Python 3.6

Added
- Support for having multiple LunarTopo frames at once
- Deletion of old LunarTopo frame variables from kernel pool when MoonLocation deleted
- Cleaned up code in topo.py to reduce code duplication.

Fixed
- Transformations involving MoonLocation objects holding multiple positions.
- Transformations from LunarTopo to LunarTopo (at a different place).

Deprecated

Added
- Corrected transformations for nearby objects (in the solar system)

Fixed
- Bug related to multiple obstimes in topo transformations

Added
- More references to README

Changed
- Keep pck and fk kernels in the repository, instead of caching.

- Initial release.