[Cashtab] [chronik tx history p13] add unit tests for airdrop and encrypted msgs

Summary:
T2447

Depends on D12137

Add unit tests for encrypted txs and airdrop txs.

It's not practical to migrate unit tests from legacy parsed txs because the wallet mocks have changed. So instead, new unit tests are added to cover these types of txs before deprecating the old functions.

Test Plan: Review new unit tests and npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D12139