[lib] Don't fetch the same ENS names simultaneously

Summary:
Sometimes when some interfaces load, there will be multiple places where the same ENS name needs to be fetched. Currently, that results in multiple queries for the same ENS name.

This diff makes sure we don't query for the same ENS name simultaneously.

Depends on D6430

Test Plan: cd lib && ALCHEMY_API_KEY=... yarn test utils/ens-cache.test.js

Reviewers: atul

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D6431