paymentsdb+sqldb: add migration related query

Add a migration specific query which allows to set the failure
reason when inserting a payment into the db.

sqldb/sqlc/querier.go

@@ -54,6 +54,9 @@ type Querier interface {
 	// Used to avoid fetching redundant payment data when processing multiple
 	// attempts for the same payment.
 	FetchPaymentsByIDs(ctx context.Context, paymentIds []int64) ([]FetchPaymentsByIDsRow, error)
+	// Migration-specific batch fetch that returns payment data along with HTLC
+	// attempt counts for structural validation during KV to SQL migration.
+	FetchPaymentsByIDsMig(ctx context.Context, paymentIds []int64) ([]FetchPaymentsByIDsMigRow, error)
 	// FetchPendingInvoices returns all invoices in a pending state (open or
 	// accepted). The invoices_state_idx index on the state column makes this a
 	// fast index scan rather than a full table scan.
@@ -178,6 +181,11 @@ type Querier interface {
 	InsertPaymentHopCustomRecord(ctx context.Context, arg InsertPaymentHopCustomRecordParams) error
 	// Insert a payment intent for a given payment and return its ID.
 	InsertPaymentIntent(ctx context.Context, arg InsertPaymentIntentParams) (int64, error)
+	// Migration-specific payment insert that allows setting fail_reason.
+	// Normal InsertPayment forces fail_reason to NULL since new payments
+	// aren't failed yet. During migration, we're inserting historical data
+	// that may already be failed.
+	InsertPaymentMig(ctx context.Context, arg InsertPaymentMigParams) (int64, error)
 	InsertRouteHop(ctx context.Context, arg InsertRouteHopParams) (int64, error)
 	InsertRouteHopAmp(ctx context.Context, arg InsertRouteHopAmpParams) error
 	InsertRouteHopBlinded(ctx context.Context, arg InsertRouteHopBlindedParams) error