feat: improve rules_js parity

tests/js_compat_test/helper.ts

@@ -0,0 +1,6 @@
+import { readFileSync } from "node:fs";
+
+export function helperMessage(): string {
+  const payload = readFileSync(new URL("./payload.txt", import.meta.url), "utf8").trim();
+  return `helper:${payload}`;
+}