chg: test: Refactor the cyclic_glue ans5 response server

Use the small record-builder helpers and module-style dnspython imports of the other `isctest.asyncserver` servers. Switching to `QnameQtypeHandler` also makes the declared qtypes take effect — a plain `QnameHandler` ignores them — restricting the referrals to the A queries the test actually sends.

Merge branch 'stepan/cyclic_glue-asyncserver-cleanup' into 'main'

See merge request isc-projects/bind9!12525