[mock-chronik-client] implement ts

Summary:
Need TS to keep up with Agora and Chronik methods

Ended up being more involved than I originally planned.

I've been putting this off because I wasn't sure how useful this lib would be. But, it's become insdispensable for any app that uses ChronikClient and is can't or won't support integrated regtest.

This is a breaking change. CI confirms that everything it breaks in the monorepo is fixed.

This module is much more effective and useful for tests now.

Test Plan: npm test, npm run build

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17332