chg: dev: Do not attach authdb

The authdb variable is used either to check that, on restarts, we
do not cross to a different zone unless recursion is enabled, and to
lookup the zone version when filling the additional section.

Neither use requires the pointer to be attached, and attaching the
pointer causes scalability issues. This commit solves the problem by
turning the pointer into an integer id.

Merge branch 'alessio/authdb-version-lookup' into 'main'

See merge request isc-projects/bind9!12375