adding IP address benchmark

[lemire]

adding the bench_ip benchmark from #349 (credit in the commit to @shikharish

In my test, we are at the same speed as std::from_chars (Apple LLVM, Apple M4).

parse_ip_std_fromchars                   :   0.58 GB/s   40.3 Ma/s  24.82 ns/d   4.41 GHz  109.60 c/d  489.57 i/d   7.67 c/b  34.28 i/b   4.47 i/c 
parse_ip_fastfloat                       :   0.59 GB/s   41.0 Ma/s  24.40 ns/d   4.50 GHz  109.82 c/d  476.18 i/d   7.69 c/b  33.34 i/b   4.34 i/c 
sink=3749209294