[backport] [backport#15780] wallet: add cachable amounts for caching credit/debit values
https://github.com/bitcoin/bitcoin/pull/15780/commits/c9e6e7ed79886b702614e627a966fc9a4850f8f0
Backport of Core [[https://github.com/bitcoin/bitcoin/pull/15780 | PR15780]]
Test Plan:
- ninja check-all
Differential Revision: https://reviews.bitcoinabc.org/D6347