retdns 0.2.1 — request and storage limits

Incoming lookups now have concurrency and rate limits, so a burst of requests cannot start unlimited registry work. Busy servers return server_busy.

Lookup history is capped at 50,000 events by default, including databases opened after upgrading. The seven-day retention limit still applies. Under heavy load, the count cap shortens the popularity window. Anonymous lookups can influence the ranking; use a curated bulk policy if that matters for your service.

Names, addresses, TTLs and the wire protocol stay the same. This is still experimental software. The attached wheel and source archive are version 0.2.1.