ensure wider range of testing for testRoundTripFuzzPow

[thedavidmeister]

                    {
                        (, int256 exponentInv) = inv.unpack();
                        vm.assume(exponentInv <= 8e8);
                    }

this rather arbitrary limit should not exist in the fuzz round trip test, it is here due to an overflow in pow due to using exponentiation by squaring on an integer value