Function happy_dial_via 

pub async fn happy_dial_via(
    dns: &DnsCache,
    host: &str,
    port: u16,
    delay: Option<Duration>,
) -> Result<TcpStream>

The cached variant of happy_dial for the pooled connector (PERF-05, #170). Resolution runs through the shared DnsCache (async hickory with TTL + negative caching) instead of the blocking-pool getaddrinfo of tokio::net::lookup_host; the RFC 8305 racing and NODELAY behavior are identical. IP-literal hosts skip DNS via the cache’s short-circuit. The active health probes keep using happy_dial (system resolver) — they are a background, infrequent path and do not share the pooled connector’s cache.