[ecash-script] Add unit tests to CI

Summary:
T3183

Add unit tests to CI.

Create .gitignore with unit test coverage artifacts

Test Plan:
npm test
Call the bot

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14012