new: dev: Add DTRACE probes to the delegation cache

The new delegation cache, which stores NS-based and DELEG-based delegations per view, is now instrumented
with static user-space tracing probes so that cache hit rate, insertion and lookup latency, eviction pressure
under memory limits, and removals triggered by rndc flush-delegation can be observed on a running named.

Merge branch 'ondrej/delegdb-dtrace-probes' into 'main'

See merge request isc-projects/bind9!11855