Low: various: Correct some printf specifiers

As of 18a93372, we can use the 'z' modifier for size_t and ssize_t. So
here we take advantage of that to avoid some (long long) casts.

We also correct some incorrect specifiers (signed vs. unsigned, and
using proper macros from inttypes.h).

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>