backport: Merge bitcoin#26715#7034

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vijaydasmp wants to merge 2 commits intodashpay:developfrom

vijaydasmp:Dec_2025_2

Commits on Dec 4, 2025

Merge bitcoin/bitcoin#26715: Introduce `MockableDatabase` for wallet unit tests

fanquake
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vijaydasmp
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Merge bitcoin/bitcoin#27665: walletdb: Remove unused CreateMockWalletDatabase

fanquake
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vijaydasmp
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