Returns the directory where taxify stores downloaded backbone and
enrichment .vtr files. By default this is the platform-appropriate
per-user cache returned by tools::R_user_dir() (available since R 4.0).
Details
The location can be overridden, in order of precedence, by the
taxify.data_dir option (getOption("taxify.data_dir")) or the
TAXIFY_DATA_DIR environment variable. This is useful to point taxify at
a shared cache, or at the small bundled example database returned by
taxify_example_data().