smartcar/typescript-backend-sdks ? reverse-engineered prompt

Build me a TypeScript backend SDK repo for Smartcar that helps apps handle webhooks and vehicle signal data cleanly.

I want one package that can parse Smartcar webhook payloads, verify webhook signatures, and create the challenge response for endpoint verification. I also want a second package that makes it easy to pull specific vehicle signals out of an array with good type safety, so things like battery level, location, odometer, and charging data are easy to work with.

Please include a simple example app that shows how these two pieces work together in an Express server, with a webhook route that verifies requests, handles the verification challenge, and processes vehicle state updates. Make sure the code is strongly typed and easy to use in backend projects. If you need current details from the Smartcar docs or OpenAPI specs, look them up online first.