Report where the cache lives and how big it is. The result includes cachem's
info() fields (such as dir, max_size and max_age) plus enabled,
n_entries and size_mb. Entries written by older epidatr versions share
the directory and are counted; use clear_cache to remove them. When the
cache is off, the directory it would use is inspected instead.
See also
set_cache to start a new cache (and general caching info),
clear_cache to delete the cache and set a new one, and disable_cache to
disable without deleting