bolthelper.go
func (db DB) Begin(writable bool) (Tx, error) {
	tx, err := db.DB.Begin(writable)
	return Tx{tx}, errorsp.WithStacks(err)
}
func (db DB) Begin(writable bool) (Tx, error) {
	tx, err := db.DB.Begin(writable)
	return Tx{tx}, errorsp.WithStacks(err)
}
// Begin wraps bolt.DB.Begin.