Add rejectUnauthorized to RequestOptions

[Copilot]

rejectUnauthorized was only on a private UrllibRequestOptions interface in src/index.ts, not on the exported RequestOptions type. Users couldn't pass it without TypeScript errors when typing their options against RequestOptions.

• Moved rejectUnauthorized?: boolean from private UrllibRequestOptions to the public RequestOptions type in src/Request.ts
• UrllibRequestOptions now inherits it via extends RequestOptions

import urllib, { RequestOptions } from 'urllib';

const opts: RequestOptions = {
  rejectUnauthorized: false, // now valid
  dataType: 'json',
};
const response = await urllib.request(url, opts);