fix: add io as named exports

The TypeScript (build/index.d.ts) and ES modules exports did not match,
which caused issues with webpack and ts-loader.

Related: #1396

wrapper.mjs

@@ -1,4 +1,5 @@
 import io from "./build/index.js";
 
 export const Manager = io.Manager;
+export const io = io;
 export default io;