Would there be positive interest rates on bonds in a world with absolutely no risk no default risk, maturity risk, and so on? Why would a, borrower be willing to pay and a lender demand, a positive interest rate in such a no-risk world?

Yes, there probable a positive rate of interest in a risk-free world.  This is for the reason that regardless of risk, lenders of money ought to postpone spending during the time the money is loaned. Lenders, after that, lose the opportunity to spend their money for that period of time. To compensate for the cost of losing investment opportunities while they postpone their spending, borrowers pay and lenders demand a basic rate of return that the real rate of interest.