censobr does not remember custom cache directory between sessions

Today, users can set set a local directory for {censobr} with censobr::set_censobr_cache_dir() . However, this path only works within the current R session, so users need to repeatedly set the cache directory every new session.

The idea here is that the user can set a local directory for {censobr} with censobr::set_censobr_cache_dir() once, and the package saves that path to the package enviroment.