[chronik-client] Support isFinal key for Tx

Summary:
Add the now-in-chronik isFinal key to the Tx object returned by chronik-client

Confirm with tests

Update ecash-lib tests and Cashtab types to match the change (otherwise this diff will break those apps).

Test Plan:
npm test and CI tests for downstream libs / apps

cd apps/ecash-herald && npm test, works

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D17177