chg: dev: Simplify and modernize the radix tree implementation

Refactor the radix tree used for ACL IP prefix matching, originally imported
from the MRT routing toolkit in 1999 and never modernized.  Node size drops
from 100+ bytes across two allocations to 64 bytes in a single cache line.
Expand the unit test suite.

Merge branch 'ondrej/refactor-isc_radix-unit' into 'main'

See merge request isc-projects/bind9!11731