Improve URL checks to reduce false-negatives

This commit improves the URL health checking mechanism to reduce false
negatives.

- Treat all 2XX status codes as successful, addressing issues with codes
  like `204`.
- Exclude URLs within Markdown inline code blocks.
- Send the Host header for improved handling of webpages behind proxies.
- Improve formatting and context for output messages.
- Fix the defaulting options for redirects and cookie handling.
- Add URL exclusion support for non-responsive URLs.
- Update the user agent pool to modern browsers and platforms.
- Improve CI/CD workflow to respond to modifications in the
  `test/checks/external-urls` directory, offering immediate feedback on
  potential impacts to the external URL test.
- Add support for randomizing TLS fingerprint to mimic various clients
  better, improving the effectiveness of checks. However, this is not
  fully supported by Node.js's HTTP client; see nodejs/undici#1983 for
  more details.
- Use `AbortSignal` instead of `AbortController` as more modern and
  simpler way to handle timeouts.

tests/checks/external-urls/StatusChecker/FetchWithTimeout.ts

@@ -2,13 +2,13 @@ export async function fetchWithTimeout(
   url: string,
   timeoutInMs: number,
   init?: RequestInit,
-): Promise<Response> {
-  const controller = new AbortController();
+): ReturnType<typeof fetch> {
   const options: RequestInit = {
     ...(init ?? {}),
-    signal: controller.signal,
+    signal: AbortSignal.timeout(timeoutInMs),
   };
-  const promise = fetch(url, options);
-  const timeout = setTimeout(() => controller.abort(), timeoutInMs);
-  return promise.finally(() => clearTimeout(timeout));
+  return fetch(
+    url,
+    options,
+  );
 }