[cashtab] fix useWallet test

Summary:
Depends on D11258.
This adds useWallet test back, with a custom environment to handle issues with jest27 and Uint8Array.

Test Plan:
npm install
npm test

ALL tests should pass.

Reviewers: bytesofman, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: bytesofman, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D11260