invoices/sql: replace catch-all GetInvoice with indexed lookups

The GetInvoice query used an OR IS NULL pattern for each filter
parameter:

  WHERE (i.hash = $1 OR $1 IS NULL)
    AND (i.payment_addr = $2 OR $2 IS NULL)

SQLite's query planner decides on an execution plan at prepare time,
before seeing any parameter values. Because either condition can be
trivially true when its parameter is NULL, the planner conservatively
falls back to a full table scan rather than using the unique indexes on
hash and payment_addr. This caused every invoice lookup and update on
the hot path (HTLC settlement) to scan the entire invoices table.

Replace the single catch-all query with three dedicated queries, each
using a direct equality on a uniquely constrained column:

- GetInvoiceByHash:  WHERE hash = $1
- GetInvoiceByAddr:  WHERE payment_addr = $1  (new, covers AMP path)
- GetInvoiceBySetID: existing, unchanged

Update getInvoiceByRef to route to the appropriate query based on which
fields are present in the InvoiceRef. When both hash and payment address
are provided, we look up by hash and then verify the returned invoice's
payment address matches.

GetInvoice is now unused and removed from the SQLInvoiceQueries
interface.

sqldb/sqlc/invoices.sql.go

@@ -476,6 +476,38 @@ func (q *Queries) GetInvoice(ctx context.Context, arg GetInvoiceParams) ([]Invoi
 	return items, nil
 }
 
+const getInvoiceByAddr = `-- name: GetInvoiceByAddr :one
+SELECT i.id, i.hash, i.preimage, i.settle_index, i.settled_at, i.memo, i.amount_msat, i.cltv_delta, i.expiry, i.payment_addr, i.payment_request, i.payment_request_hash, i.state, i.amount_paid_msat, i.is_amp, i.is_hodl, i.is_keysend, i.created_at
+FROM invoices i
+WHERE i.payment_addr = $1
+`
+
+func (q *Queries) GetInvoiceByAddr(ctx context.Context, paymentAddr []byte) (Invoice, error) {
+	row := q.db.QueryRowContext(ctx, getInvoiceByAddr, paymentAddr)
+	var i Invoice
+	err := row.Scan(
+		&i.ID,
+		&i.Hash,
+		&i.Preimage,
+		&i.SettleIndex,
+		&i.SettledAt,
+		&i.Memo,
+		&i.AmountMsat,
+		&i.CltvDelta,
+		&i.Expiry,
+		&i.PaymentAddr,
+		&i.PaymentRequest,
+		&i.PaymentRequestHash,
+		&i.State,
+		&i.AmountPaidMsat,
+		&i.IsAmp,
+		&i.IsHodl,
+		&i.IsKeysend,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
 const getInvoiceByHash = `-- name: GetInvoiceByHash :one
 SELECT i.id, i.hash, i.preimage, i.settle_index, i.settled_at, i.memo, i.amount_msat, i.cltv_delta, i.expiry, i.payment_addr, i.payment_request, i.payment_request_hash, i.state, i.amount_paid_msat, i.is_amp, i.is_hodl, i.is_keysend, i.created_at
 FROM invoices i

sqldb/sqlc/querier.go

@@ -111,6 +111,7 @@ 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)
+	GetInvoiceByAddr(ctx context.Context, paymentAddr []byte) (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)

sqldb/sqlc/queries/invoices.sql

@@ -59,6 +59,11 @@ SELECT i.*
 FROM invoices i
 WHERE i.hash = $1;
 
+-- name: GetInvoiceByAddr :one
+SELECT i.*
+FROM invoices i
+WHERE i.payment_addr = $1;
+
 -- name: GetInvoiceBySetID :many
 SELECT i.*
 FROM invoices i