feat: hooks / events for rate-limit and ban actions

[rrd108]

Add lifecycle hooks so users can react to rate-limit and ban events.

Suggested hooks:

• onRateLimitExceeded(ip, path, count) — called when a request exceeds the limit (before ban is set)
• onBan(ip, path, duration) — called when an IP is banned
• onBannedRequest(ip, path) — called when a banned IP attempts a request

Use cases:

• Send Slack/Discord alerts on repeat offenders
• Push metrics to Prometheus/StatsD
• Write to a custom audit log
• Trigger external firewall rules (e.g., Cloudflare API block)