sweeper: relax anchor sweeping when there's no deadline pressure (#7965)

* sweep: use longer variable name for clarity in `addToState`

* sweeper: add more docs and debug logs

* sweep: prioritize smaller inputs when adding wallet UTXOs

This commit sorts wallet UTXOs by their values when using them for
sweeping inputs. This way we'd avoid locking large UTXOs when sweeping
inputs and also provide an opportunity to aggregate wallet UTXOs.

* contractcourt+itest: relax anchor sweeping for CPFP purpose

This commit changes from always sweeping anchor for a local force close
to only do so when there is an actual time pressure. After this change,
a forced anchor sweeping will only be attempted when the deadline is
less than 144 blocks.

* docs: update release notes

* itest: update test `testMultiHopHtlcLocalChainClaim` to skip CPFP

Since we now only perform CPFP when both the fee rate is higher and the
deadline is less than 144, we need to update the test to reflect that
Bob will not CPFP the force close tx for the channle Alice->Bob.

* itest: fix `testMultiHopRemoteForceCloseOnChainHtlcTimeout`

* itest: update related tests to reflect anchor sweeping

This commit updates all related tests to reflect the latest anchor
sweeping behavior. Previously, anchor sweeping is always attempted as
CPFP when a force close is broadcast, while now it only happens when the
deadline is less than 144. For non-CPFP purpose sweeping, it will happen
after one block is mined after the force close transaction is confirmed
as the anchor will be resent to the sweeper with a floor fee rate, hence
making it economical to sweep.

itest/lnd_channel_backup_test.go

@@ -783,16 +783,15 @@ func runChanRestoreScenarioForceClose(ht *lntest.HarnessTest, zeroConf bool) {
 		ht, crs.password, crs.mnemonic, multi, dave,
 	)
 
-	// We now wait until both Dave's closing tx and sweep tx have shown in
-	// mempool.
-	ht.Miner.AssertNumTxsInMempool(2)
+	// We now wait until both Dave's closing tx.
+	ht.Miner.AssertNumTxsInMempool(1)
 
 	// Now that we're able to make our restored now, we'll shutdown the old
 	// Dave node as we'll be storing it shortly below.
 	ht.Shutdown(dave)
 
 	// Mine a block to confirm the closing tx from Dave.
-	ht.MineBlocksAndAssertNumTxes(1, 2)
+	ht.MineBlocksAndAssertNumTxes(1, 1)
 
 	// To make sure the channel state is advanced correctly if the channel
 	// peer is not online at first, we also shutdown Carol.
@@ -1412,8 +1411,9 @@ func chanRestoreViaRPC(ht *lntest.HarnessTest, password []byte,
 func assertTimeLockSwept(ht *lntest.HarnessTest, carol, dave *node.HarnessNode,
 	carolStartingBalance, daveStartingBalance int64) {
 
-	// We expect Carol to sweep her funds and also the anchor tx.
-	expectedTxes := 2
+	// We expect Carol to sweep her funds and also the anchor tx. In
+	// addition, Dave will also sweep his anchor output.
+	expectedTxes := 3
 
 	// Carol should sweep her funds immediately, as they are not
 	// timelocked.
@@ -1495,11 +1495,7 @@ func assertDLPExecuted(ht *lntest.HarnessTest,
 
 	// Upon reconnection, the nodes should detect that Dave is out of sync.
 	// Carol should force close the channel using her latest commitment.
-	expectedTxes := 1
-	if lntest.CommitTypeHasAnchors(commitType) {
-		expectedTxes = 2
-	}
-	ht.Miner.AssertNumTxsInMempool(expectedTxes)
+	ht.Miner.AssertNumTxsInMempool(1)
 
 	// Channel should be in the state "waiting close" for Carol since she
 	// broadcasted the force close tx.
@@ -1515,7 +1511,8 @@ func assertDLPExecuted(ht *lntest.HarnessTest,
 	ht.RestartNode(dave)
 
 	// Generate a single block, which should confirm the closing tx.
-	ht.MineBlocksAndAssertNumTxes(1, expectedTxes)
+	ht.MineBlocksAndAssertNumTxes(1, 1)
+	blocksMined := uint32(1)
 
 	// Dave should consider the channel pending force close (since he is
 	// waiting for his sweep to confirm).
@@ -1532,6 +1529,14 @@ func assertDLPExecuted(ht *lntest.HarnessTest,
 
 		// Mine Dave's anchor sweep tx.
 		ht.MineBlocksAndAssertNumTxes(1, 1)
+		blocksMined++
+
+		// The above block will trigger Carol's sweeper to reconsider
+		// the anchor sweeping. Because we are now sweeping at the fee
+		// rate floor, the sweeper will consider this input has
+		// positive yield thus attempts the sweeping.
+		ht.MineBlocksAndAssertNumTxes(1, 1)
+		blocksMined++
 
 		// After Carol's output matures, she should also reclaim her
 		// funds.
@@ -1539,7 +1544,7 @@ func assertDLPExecuted(ht *lntest.HarnessTest,
 		// The commit sweep resolver publishes the sweep tx at
 		// defaultCSV-1 and we already mined one block after the
 		// commitmment was published, so take that into account.
-		ht.MineBlocks(defaultCSV - 1 - 1)
+		ht.MineBlocks(defaultCSV - blocksMined)
 		ht.MineBlocksAndAssertNumTxes(1, 1)
 
 		// Now the channel should be fully closed also from Carol's POV.
@@ -1561,21 +1566,33 @@ func assertDLPExecuted(ht *lntest.HarnessTest,
 		// Dave should sweep his funds immediately, as they are not
 		// timelocked. We also expect Dave to sweep his anchor, if
 		// present.
-		ht.Miner.AssertNumTxsInMempool(expectedTxes)
+		if lntest.CommitTypeHasAnchors(commitType) {
+			ht.MineBlocksAndAssertNumTxes(1, 2)
+		} else {
+			ht.MineBlocksAndAssertNumTxes(1, 1)
+		}
 
-		// Mine the sweep tx.
-		ht.MineBlocksAndAssertNumTxes(1, expectedTxes)
+		blocksMined++
 
 		// Now Dave should consider the channel fully closed.
 		ht.AssertNumPendingForceClose(dave, 0)
 
+		// The above block will trigger Carol's sweeper to reconsider
+		// the anchor sweeping. Because we are now sweeping at the fee
+		// rate floor, the sweeper will consider this input has
+		// positive yield thus attempts the sweeping.
+		if lntest.CommitTypeHasAnchors(commitType) {
+			ht.MineBlocksAndAssertNumTxes(1, 1)
+			blocksMined++
+		}
+
 		// After Carol's output matures, she should also reclaim her
 		// funds.
 		//
 		// The commit sweep resolver publishes the sweep tx at
-		// defaultCSV-1 and we already mined one block after the
+		// defaultCSV-1 and we already have blocks mined after the
 		// commitmment was published, so take that into account.
-		ht.MineBlocks(defaultCSV - 1 - 1)
+		ht.MineBlocks(defaultCSV - blocksMined)
 		ht.MineBlocksAndAssertNumTxes(1, 1)
 
 		// Now the channel should be fully closed also from Carol's