Instead of having to manually stub packages that should not be
downloaded we instead automatically stub all packages (except a small
list of whitelisted ones). Tests can re-introduce the real package by
using the `realPkgs` module argument.
Some fish plugins such as https://github.com/acomagu/fish-async-prompt
require that starship be initialized as non-interactive.
When the `programs.starship.enableInteractive` option is enabled,
starship is initialized at the end of the init script, outside the
interactive block.