[v0.1.x-branch] Backport #1066: txconfirm: release abandoned fee input on CPFP reselect

[github-actions]

Backport of #1066

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Closes #664.

Problem

In broadcastWithCPFP, when the precise per-input vsize recompute grows
the package fee enough to push the originally selected fee input's change
below the dust limit, the broadcaster reselects a larger fee input — but
it had already reserveFeeInput'd (and wallet-LeaseOutput'd) the
original before the reselect and never released it. The abandoned UTXO
stays reserved and wallet-leased for the parent's whole lifetime (or until
DefaultFeeInputLeaseExpiry), even though the CPFP child only ever spends
the reselected input. It's a spurious UTXO lock (not fund loss) that
starves other fee selections.

Fix

Release the abandoned input's reservation + wallet lease
(releaseFeeOutpoint) when the reselect lands on a different outpoint.

The caveat that makes this non-trivial: selectFeeInput can
legitimately return a carried-over reservation on a fee bump — TRUC
package RBF requires the replacement child to double-spend the previous
child's fee input, so that input must stay reserved. The release therefore
skips a carried-over input: feeOutpointReserved records whether the input
was already reserved before the (idempotent) re-reservation, so a
freshly-selected-and-abandoned input is released while a carried-over one
is left intact.

Testing

TestCPFPReselectReleasesAbandonedFeeInput drives the exact reselect path
(a P2PKH fee input heavier than the OP_TRUE change proxy grows the fee and
forces a reselect off the small UTXO) and asserts the abandoned input is
dropped from the in-memory reservation set and its wallet lease is
released, while the reselected input stays reserved. It fails on main and
passes with the fix. Full txconfirm suite + lint-changed-local green.

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