make bounded() unambiguous

std::size_t is the unsigned integer type of the result of the sizeof
operator

this can make the bounded call ambiguous as it either sports
an int(int,int) signature or an quint32(quint32,quint32) signature. with
size_t being unsigned and 0 being int it's not necessarily clear to the
compiler which overload to use, so make it clear by using usigned
everywhere.
this specifically fixes arm32 compatibility on ubuntu 20.04