Sets up the optional Hipparcos star catalog for fixed-star features.
Usage: mix eph.setup_stars mix eph.setup_stars --force
Downloads hip_main.dat (VizieR catalog I/239 / ESA Hipparcos) into
priv/stars/ by default. Fixed-star APIs are optional until this file exists.
Manual setup: download hip_main.dat from the
VizieR I/239 catalog page
and place it at the path printed by this task.