fix: widen reconnectTimer type for canary compatibility

Deno canary's TypeScript types now expose `setTimeout` as returning a
`Timeout` object instead of `number`, which trips `TS2322` against the
existing `let reconnectTimer: number` declaration. The variable is only
passed back to `clearTimeout`, so widen it to the inferred return type.

Fixes the canary CI failure on this branch (unchanged behavior).

Author: fibibot

packages/fresh/src/runtime/client/dev_hmr.ts

@@ -3,7 +3,7 @@ import { IS_BROWSER } from "../shared.ts";
 let ws: WebSocket;
 let revision = 0;
 
-let reconnectTimer: number;
+let reconnectTimer: ReturnType<typeof setTimeout>;
 const backoff = [
   // Wait 100ms initially, because we could also be
   // disconnected because of a form submit.