staticaddr/loopin: reject expiring deposits

Manual static-address loop-ins can name explicit deposit outpoints.
Those paths only checked that deposits were available. An old deposit
could get a quote, then fail server init.

Apply the same swappability and expiry runway check used by automatic
selection to manual quotes and initiation. The client now rejects before
contacting the server.

build: bump lnd to v0.21

test: refresh route hint preservation comments

lndclient now forwards route hints through AddInvoice. These tests
assert that Loop preserves explicit hints on generated loop-in invoices.
Remove stale comments that described the old wrapper behavior as
dropping hints.

loopd: recover confirmed htlcs with direct sweep

loopd: recover confirmed htlcs with direct sweep

loopd: recover confirmed htlcs with direct sweep

staticaddr: model pending withdrawals

Represent withdrawal txids as optional in the domain model and keep
pending withdrawals visible through GetAllWithdrawals.

Pending rows now surface nil and zero values in Go and empty and zero
defaults over RPC, while malformed non-NULL txids still fail loudly.

Also sync godoc's with how it actually behaves: returns pending withdraws
in addition to finalized ones.

utils: accept raw keys in MuSig2Sign

utils: accept raw keys in MuSig2Sign

withdraw: persist tx before state transitions

Persist finalized withdrawal tx pointers to all selected deposits before
triggering state transitions. This avoids restart races where deposits can
remain in WITHDRAWING without a recoverable finalized tx reference.

Recovery now groups withdrawing deposits by tx hash and restores missing tx
pointers when there is exactly one in-flight withdrawal cluster. Recovered
pointers are written back so subsequent restarts remain stable.

Add a regression test which exercises recoverWithdrawals end-to-end and verifies
restart recovery for WITHDRAWING deposits missing FinalizedWithdrawalTx.