[9.18] [CVE-2025-13878] sec: test: Add a regression test for the BRID/HHIT crash

Add two short records to example.com.db that cause assertion failures
when converted to wire form.

The checks added to tests.sh are technically not required: the relevant
assertion failures are already hit when the zone is transferred out of
ns1.

Update the relevant unit tests with 1-byte records.

Co-authored-by: Mark Andrews <marka@isc.org>
Closes #5616

Backport of MR !11522

Merge branch 'backport-5616-add-brid-hhit-towire-tests-9.18' into 'bind-9.18'

See merge request isc-projects/bind9!11524