lnwallet: define helper func to coop close conf scaling

We have two versions: for itests, we just use one conf, but in prod,
we'll scale the number of confirmations.

lnwallet/confscale_integration.go

@@ -0,0 +1,13 @@
+//go:build integration
+// +build integration
+
+package lnwallet
+
+import "github.com/btcsuite/btcd/btcutil"
+
+// CloseConfsForCapacity returns the number of confirmations to wait
+// before signaling a cooperative close. Under integration tests, we
+// always return 1 to keep tests fast and deterministic.
+func CloseConfsForCapacity(capacity btcutil.Amount) uint32 { //nolint:revive
+	return 1
+}