mapReader = (reader, transform) => {
  async function* transformGenerator() {
    for await (const value of reader) {
      yield transform(value);
    }
    return undefined;
  }
  harden(transformGenerator);
  return harden(transformGenerator());
}
@template TIn
@template TOut
@param {import('./types.js').Reader<TIn>} reader
@param {(value: TIn) => TOut} transform
@returns {import('./types.js').Reader<TOut>}