htlcswitch: define state machine for quiescence

htlcswitch: add sendOwedStfu method to quiescer

go.mod

@@ -36,7 +36,7 @@ require (
 	github.com/lightningnetwork/lightning-onion v1.2.1-0.20240712235311-98bd56499dfb
 	github.com/lightningnetwork/lnd/cert v1.2.2
 	github.com/lightningnetwork/lnd/clock v1.1.1
-	github.com/lightningnetwork/lnd/fn v1.2.3
+	github.com/lightningnetwork/lnd/fn v1.2.5
 	github.com/lightningnetwork/lnd/healthcheck v1.2.6
 	github.com/lightningnetwork/lnd/kvdb v1.4.11
 	github.com/lightningnetwork/lnd/queue v1.1.1