Returns the directory used to store cached model artifacts. By default this is
a platform-appropriate user cache path from tools::R_user_dir("writeAlizer","cache").
If the option writeAlizer.cache_dir is set to a non-empty string, that
location is used instead. This makes it easy to redirect the cache during tests
or examples (e.g., to tempdir()).
Details
The override must be one non-missing character string. An empty string uses the default. Choose a dedicated directory: clearing the cache deletes all of its contents.