Returns results from the in-memory cache, filtered by ids if given.
Cache must be created first using crant_meta_create_cache().
Details
crant_meta() never queries databases directly.
If ids are given, filters the meta table by root_id.
Examples
if (FALSE) { # \dontrun{
crant_meta_create_cache() # build the cache
all_meta <- crant_meta() # retrieve all
} # }
