Performance audit: tx_revision bumps on every new block because each tx's confirmation count rises, so
the History tab's groupByTxid + merge + sort + deep-copy display cache fully rebuilt once per ~36s block
on the UI thread, even when nothing but the counts changed.
Add WalletState::tx_structure_revision, bumped alongside tx_revision EXCEPT when setTransactionsIfChanged
sees a pure confirmation-count delta (new sameTransactionLayout: every row equal ignoring the confirmation
COUNT, but the pending/confirmations==0 state — which drives the pending-first sort and shield merge — must
still match). Every other writer bumps both (conservative default). The History tab's groups cache and
display cache now key on tx_structure_revision; on a confirmation-only delta it patches dtx.confirmations
in place (rows, order and indices into state.transactions are unchanged) instead of rebuilding, and re-stamps
the filter snapshot so "export current filter" stays valid. Displayed confirmations still update every block.
No fund path touched; display/caching only. Test: testTxStructureRevision.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>