CLSA-2026-1787221736 bind: Fix of 2 CVEs

CVE-2023-6516: bound the memory used to queue RBTDB tree-pruning events, so that recursive query patterns which continuously trigger cache-database maintenance can no longer exceed max-cache-size and exhaust host memory DoS - CVE-2023-6516 follow-up: make the tree-pruning queue per-node-lock...