[GH #828] Optimize print_n/i and say_n/i

print_n/nc/i/ic and the say variants go through a full Parrot_io_printf with
3 va_start/va_end scenarios and a custom format string parser,
and through char* -> STRING->char* conversion until the fixed
FLOATVAL_FMT or INTVAL_FMT printf is done.
Just to print a single int or number.

This also lost precision for non-double floatval's - if cast to (double).
Now avoided.