make a new package for helpers

packages/helpers/reject-after.ts

@@ -0,0 +1,10 @@
+import { setTimeout } from "node:timers/promises"
+import { toError } from "./to-error.js"
+
+export async function rejectAfter(
+  timeMs: number,
+  error: unknown = `rejected after ${timeMs}ms`,
+): Promise<never> {
+  await setTimeout(timeMs)
+  throw toError(error)
+}