fix: extend Retry-After parsing to RDAP 503 and fix block pattern across newlines

- Parse `Retry-After` on RDAP `503` responses (previously only `429`), exposing `retryAfterMs` on the attempt and on the top-level result when `rdapOnly` makes it terminal
- Fix the WHOIS `BLOCK_PATTERNS` regex to use `[\s\S]` instead of `.` so a block notice that spans multiple lines (e.g. `"Your IP address\nhas been blocked"`) is still classified as `blocked`
- Update README to document `retryAfterMs` on `LookupResult`, clarify `rate_limited` / `blocked` / `unparseable` semantics, and note referral-host validation behaviour

src/whois/throttle.test.ts

@@ -15,6 +15,7 @@ describe("detectWhoisRefusal", () => {
   it.each([
     "Requests of this client are not permitted. Please use https://www.nic.ch/whois/ for queries.",
     "Your IP address has been blocked",
+    "Your IP address\nhas been blocked",
   ])("classifies %j as blocked", (text) => {
     expect(detectWhoisRefusal(text)).toBe("blocked");
   });

src/whois/throttle.ts

@@ -17,7 +17,7 @@ const THROTTLE_PATTERNS: RegExp[] = [
 // Permanent: this client is refused outright, so retrying will not help.
 const BLOCK_PATTERNS: RegExp[] = [
   /requests\s+of\s+this\s+client\s+are\s+not\s+permitted/i, // .ch/.li
-  /\b(your|this)\s+(ip|address|client)\b.{0,60}\b(blocked|banned|blacklisted|not\s+permitted)\b/i,
+  /\b(your|this)\s+(ip|address|client)\b[\s\S]{0,60}\b(blocked|banned|blacklisted|not\s+permitted)\b/i,
 ];
 
 /**