[Cashtab] Show XECX sweeper balance and notice if user redemption will not be instant

Summary:
XECX redemptions may not be instant if the user is looking to redeem more XECX than the redemptions hot wallet can afford. Show a notice when this case occurs.

Since we need more specific conditional rendering for XECX redemptions, improve the XECX redemption modal (customize it so it is not identical to the normal listing modal).

Sidebar: In developing here, noticed a pattern where large amounts will often get the "agora quantity error" -- i.e. if you create an agora partial with the minAcceptAtoms the same as offeredAtoms, often the partial itself will end up with minAcceptAtoms > offeredAtoms. Needs to be fixed at the lib level.

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D17775