itest: add new coop close rbf itest

This ensures that during the RBF process, if one confirms, a re-org
occurs, then another confirms, that we'll properly detect this case.

itest/lnd_funding_test.go

@@ -1272,8 +1272,17 @@ func testChannelFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	// Make sure Carol sees her to_remote output from the force close tx.
 	ht.AssertNumPendingSweeps(carol, 1)
 
-	// We need to wait for carol initiating the sweep of the to_remote
-	// output of chanPoint2.
+	// Wait for Carol's sweep transaction to appear in the mempool. Due to
+	// async confirmation notifications, there's a race between when the
+	// sweep is registered and when the sweeper processes the next block.
+	// The sweeper uses immediate=false, so it broadcasts on the next block
+	// after registration. Mine an empty block to trigger the broadcast.
+	ht.MineEmptyBlocks(1)
+
+	// Now the sweep should be in the mempool.
+	ht.AssertNumTxsInMempool(1)
+
+	// Now we should see the unconfirmed UTXO from the sweep.
 	utxo := ht.AssertNumUTXOsUnconfirmed(carol, 1)[0]
 
 	// We now try to open channel using the unconfirmed utxo.
@@ -1329,6 +1338,11 @@ func testChannelFundingWithUnstableUtxos(ht *lntest.HarnessTest) {
 	// Make sure Carol sees her to_remote output from the force close tx.
 	ht.AssertNumPendingSweeps(carol, 1)
 
+	// Mine an empty block to trigger the sweep broadcast (same fix as
+	// above).
+	ht.MineEmptyBlocks(1)
+	ht.AssertNumTxsInMempool(1)
+
 	// Wait for the to_remote sweep tx to show up in carol's wallet.
 	ht.AssertNumUTXOsUnconfirmed(carol, 1)