Returns {count, sum, 0.5, 0.95, 0.99} in seconds for Prometheus
summary exposition. Companion to the existing stats() (milliseconds).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Each listener now tracks chain setup latency independently via a
dict[str, LatencyTracker] on Metrics. The global aggregate stays for
summary output. /status embeds per-listener latency on each listener
entry; /metrics includes a listener_latency map keyed by host:port.
Add RateTracker (rolling deque, events/sec) and LatencyTracker (circular
buffer, p50/p95/p99 in ms) to the Metrics class. Both are recorded in
_handle_client and exposed via summary(), to_dict(), /status, and /metrics.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
