Failed to setting CPU affinity over 32-processor via cli arg #3231

On current version of BenchmarkDotNet implementation.
--affinity command line argument is parsed as int (signed).

So it can't accept value that over int.MaxValue value and it can't specify over 32-processor affinity.

I thought, it need to change affinity parameter to nuint (unsigned) to pass affinity as bit mask.

Note: Currently BenchmarkDotNet seems not support CPU groups. So affinity can set up to 64 logical CPU cores.