[alias-server] add consume function in new script parsing file

Summary:
T3060

Per feedback from D13916, adding consume method to new file script.js with unit tests.

Going forward, we may want to abstract this to a library. However there isn't a logical place to put it at the moment, and alias-server will the be first production user. Makes sense to keep it here and reserve the option to abstract to a libary later when additional use cases are known.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13960