Add fetchWorker for fetching off the main thread

src/workers/fetch.ts

@@ -0,0 +1,19 @@
+import { Comlink } from '@/deps.ts';
+
+import type { FetchWorker } from './fetch.worker.ts';
+
+const _worker = Comlink.wrap<typeof FetchWorker>(
+  new Worker(
+    new URL('./fetch.worker.ts', import.meta.url),
+    { type: 'module' },
+  ),
+);
+
+const fetchWorker: typeof fetch = async (input) => {
+  const url = input instanceof Request ? input.url : input.toString();
+
+  const args = await _worker.fetch(url);
+  return new Response(...args);
+};
+
+export { fetchWorker };