Fix #3094 - improve use of portable size_t/ssize_t format specifiers.

Fix #3094 - improve use of portable size_t/ssize_t format specifiers.

The header src/cc-compat.h defines portable format specifiers PRIuZ, PRIdZ, and PRIxZ. The original report highlighted the need to use these specifiers in examples/network/fetch.c.  For this commit, I checked all C source and header files not in deps/ and transitioned to the appropriate format specifier where appropriate.