txdb: fix lockedUnconfirmed if FINALIZE is inserted with block

[pinheadmz]

This is an edge case we should have addressed in #464 especially after dealing with basically the same behavior in #387. And actually if I'd written better test coverage in #387 to actually include TRANSFER and FINALIZE, we probably would've fixed all the bugs six months ago 🤷‍♂️ 😬

The issue is that in bcoin and hsd, unconfirmed includes all confirmed amounts in addition to unconfirmed amounts, they are not mutually exclusive. Normally when we send a TX, it is inserted into the database as unconfirmed. Then when we see it in a block, we update the confirmed balance but we leave the unconfirmed balance alone (it was already updated when the TX was first seen in the mempool).

During a rescan (or more explicitly, an import-from-seed or deep rescan) we never see the TX as unconfirmed -- it is inserted into the database with the block that confirms it. So to keep the unconfirmed balance in sync, we need to update that value first, and then continue with the confirmation process that updates the confirmed balance.

[coveralls]

Pull Request Test Coverage Report for Build 250320504

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.001%) to 59.231%

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Files with Coverage Reduction	New Missed Lines	%
lib/net/pool.js	1	32.63%
lib/net/peer.js	2	35.28%

Totals
Change from base Build 238010293:	0.001%
Covered Lines:	19388
Relevant Lines:	30472

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💛 - Coveralls

[pinheadmz]

rebase to 0e7865c:
clean up test re: #512 (comment)