This function is called by append_core_attr and
appends new unique_ids to the created nodes. It also keeps track of
the already used unique_ids with the dat[["_last_unique_id"]]
variable.
update_unique_ids(dat, n.new)The updated dat main list object.
Main list object containing a networkDynamic object and
other initialization information passed from netsim.
The number of new nodes to give unique_ids to.