fix: align proxy fetch typing

src/telegram/proxy.ts

@@ -5,10 +5,10 @@ export function makeProxyFetch(proxyUrl: string): typeof fetch {
   const agent = new ProxyAgent(proxyUrl);
   // undici's fetch is runtime-compatible with global fetch but the types diverge
   // on stream/body internals. Single cast at the boundary keeps the rest type-safe.
-  const fetcher = (input: RequestInfo | URL, init?: RequestInit) =>
+  const fetcher = ((input: RequestInfo | URL, init?: RequestInit) =>
     undiciFetch(input as string | URL, {
       ...(init as Record<string, unknown>),
       dispatcher: agent,
-    }) as unknown as Promise<Response>;
+    }) as unknown as Promise<Response>) as typeof fetch;
   return wrapFetchWithAbortSignal(fetcher);
 }