This change makes the code simpler as the client and wallet models are set in the constructor and are constant.
Based on #18064, only bbb33d6.
This does't change behavior.
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Concept ACK on including models in class invariants where appropriate.
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🐙 This pull request conflicts with the target branch and needs rebase.
This is based on a PR that has since been closed (#18064), itself hasn't seen any review and currently needs a rebase. If it's still relevant them I'm going to suggest re-opening it in https://github.com/bitcoin-core/gui.