coins, refactor: Assume state after SetClean in AddFlags to prevent dangling pointers

Summary:
This is a partial backport of core#30906
https://github.com/bitcoin/bitcoin/pull/30906/commits/cd0498eabc910efa3ed7a6d32e687107248bb5be

Co-authored-by: Ryan Ofsky <ryan@ofsky.org>
Depends on D18807

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18808