pub type PoolWaitObserver = fn(&str, Duration);Expand description
Notified with (pool name, time spent waiting) every time a caller
acquires a pooled connection.
A hook rather than a direct metrics call because the dependency only goes
one way: pylon-workers (which owns the Prometheus registry) depends on
this crate, so this crate can’t call into it. Whoever owns the registry
installs an observer at startup; nobody installing one costs a single
OnceLock read per checkout.