[Cashtab] Patch cancel vs buy distinction in agora partials

Summary:
Realized previous mock was wrong after testing some cancels. Seems like the isCanceled check is only for ONESHOT, need a better check for partials.

The check here is from guess and check, test driven. Works without breaking previous tests, except for one previous test that actually was a cancel, and should be broken.

Test Plan:
npm test, see screenshots

patches bought amount for agora buys (before this diff, rendered as "bought 50")
before:

after:

patches cancels previously mis-parsed as buys
before:

after:

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D16998