sqldb+invoices: create a re-usable comparion helper function

So that we can use it for comparisons in other migrations too.

sqldb/go.mod

@@ -2,11 +2,13 @@ module github.com/lightningnetwork/lnd/sqldb
 
 require (
 	github.com/btcsuite/btclog/v2 v2.0.1-0.20250602222548-9967d19bb084
+	github.com/davecgh/go-spew v1.1.1
 	github.com/golang-migrate/migrate/v4 v4.17.0
 	github.com/jackc/pgconn v1.14.3
 	github.com/jackc/pgerrcode v0.0.0-20240316143900-6e2875d9b438
 	github.com/jackc/pgx/v5 v5.3.1
 	github.com/ory/dockertest/v3 v3.10.0
+	github.com/pmezard/go-difflib v1.0.0
 	github.com/stretchr/testify v1.9.0
 	golang.org/x/exp v0.0.0-20240325151524-a685a6edb6d8
 	modernc.org/sqlite v1.29.10
@@ -19,7 +21,6 @@ require (
 	github.com/btcsuite/btclog v0.0.0-20241003133417-09c4e92e319c // indirect
 	github.com/cenkalti/backoff/v4 v4.1.3 // indirect
 	github.com/containerd/continuity v0.3.0 // indirect
-	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/docker/cli v20.10.17+incompatible // indirect
 	github.com/docker/docker v24.0.7+incompatible // indirect
 	github.com/docker/go-connections v0.4.0 // indirect
@@ -45,7 +46,6 @@ require (
 	github.com/opencontainers/image-spec v1.0.2 // indirect
 	github.com/opencontainers/runc v1.1.5 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/rogpeppe/go-internal v1.12.0 // indirect
 	github.com/sirupsen/logrus v1.9.2 // indirect