feat(db): helper for setting retrier directly

contract.go

@@ -58,6 +58,15 @@ type Tx interface {
 // A ConfigFunc function sets up a Transaction.
 type ConfigFunc func(*Transaction)
 
+// Retry sets the retrier.
+func Retry(r retry.Retry) ConfigFunc {
+	return func(t *Transaction) {
+		t.retries = r.Attempts
+		t.delay = r.Delay
+		t.method = r.Method
+	}
+}
+
 // RetryCount defines a transaction should be tried n times. If n is 0, it will
 // be set as 1.
 func RetryCount(n int) ConfigFunc {

db_test.go

@@ -38,6 +38,7 @@ func TestNewTransaction(t *testing.T) {
 		"sql.DB":        {db, nil, nil},
 		"low attempts":  {db, []dbtools.ConfigFunc{dbtools.RetryCount(-1)}, nil},
 		"delay method":  {db, []dbtools.ConfigFunc{dbtools.DelayMethod(retry.IncrementalDelay)}, nil},
+		"retrier":       {db, []dbtools.ConfigFunc{dbtools.Retry(retry.Retry{})}, nil},
 	}
 	for name, tc := range tcs {
 		tc := tc