Fix signedness warnings.
Fix signedness warnings.

Changing pow5Factor() to return uint32_t fixes MSVC warning C4018
"'>=': signed/unsigned mismatch" and Clang -Wsign-compare
"warning: comparison of integers of different signs: 'int32_t'
(aka 'int') and 'const uint32_t' (aka 'const unsigned int')".

Also fix GCC -Wformat-signedness by using %u to print uint32_t q.

ulfjack/ryu,ulfjack/ryu,ulfjack/ryu,ulfjack/ryu