gaffneyc/usps ? reverse-engineered prompt

Build me a small Ruby library for talking to the USPS WebTools API.

I want it to let me validate addresses, look up city and state from a ZIP code, look up a ZIP code from an address, and track packages. It should feel easy to use, where I can create a request object, send it, and then read a clean response back. Please include support for the USPS certification tests too, since I may need to verify my account access.

Make sure it works with a USPS username from config or from an environment variable, and add tests for the main request types and response handling. Keep the API simple and Ruby like, with good documentation in the README showing a few examples of common use, especially address validation and tracking.

If you need to check current USPS docs or response formats online to get the details right, go ahead and do that.