fmt/print: add 64-bit length modifier %Li, %Ld and %Lu

[sreimers]

With normal printf you have to use something like this:

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>

int main()
{
    uint64_t t = 1;
    
    printf("Value %" PRIu64 "\n", t);

    return 0;
}

Since uint64_t can be unsigned long int -> %lu or unsigned long long int -> %llu on 32-bit wordsize plattforms.

This PR introduces %L to handle this:

#include <re.h>

int main()
{
    uint64_t t = 1;
    
    re_printf("Value %Lu\n", t);

    return 0;
}