sqldb+invoices: Optimize invoice fetching when the reference is only a hash

The current sqlc GetInvoice query experiences incremental slowdowns during
the migration of large invoice databases, primarily due to its complex
predicate set. For this specific use case, a streamlined GetInvoiceByHash
function provides a more efficient solution, maintaining near-constant
lookup times even with extensive table sizes.

sqldb/sqlc/querier.go

@@ -24,6 +24,7 @@ type Querier interface {
 	// from different invoices. It is the caller's responsibility to ensure that
 	// we bubble up an error in those cases.
 	GetInvoice(ctx context.Context, arg GetInvoiceParams) ([]Invoice, error)
+	GetInvoiceByHash(ctx context.Context, hash []byte) (Invoice, error)
 	GetInvoiceBySetID(ctx context.Context, setID []byte) ([]Invoice, error)
 	GetInvoiceFeatures(ctx context.Context, invoiceID int64) ([]InvoiceFeature, error)
 	GetInvoiceHTLCCustomRecords(ctx context.Context, invoiceID int64) ([]GetInvoiceHTLCCustomRecordsRow, error)