[#58] change xerrors to fmt.Errorf

[kozmod]

Close #58

In cases with join for example

	if rbErr := tx.Rollback(ctx); rbErr != nil {
		err = xerrors.Errorf("transactor - call: %w", errors.Join(err, rbErr, ErrRollbackFailed))
	} else {
		err = xerrors.Errorf("transactor - call: %w", errors.Join(err, ErrRollbackSuccess))
	}

xerrors package is useless because errors.Join does not print stack trace and log/print an error's stack trace (using "%+v") does not print full stack trace of recursive calls.

At first need to change xerrors to stdlib error impl.