Improve benchmark stability with cpusets, nice, and disabling of hyper threading

[rwstauner]

This adds to run_benchmarks.rb several additional linux features which can help to make the benchmark results more reliable:

• set scheduler priority (niceness) high
• setup two cpusets, one for benchmarks and one for everything else to move existing processes off of benchmark cpu
• disable hyper threading for benchmark cpus
• move parent process off of cpu that will be used for benchmarks

You can see this improve the results when running the same ruby version twice:
it increases the number of benchmarks that compare at 1.000 on two different computers:

By putting all this logic into a module we can easily reuse it from yjit-metrics.

I think it would make sense to eventually move the existing checks for turbo into this module as well.

[rwstauner]

For the curious, it looks like it isn't finding any cpuset files in CI, it's only setting the nice value there.

[maximecb]

Looks pretty good to me but I will also tag Alan and Kokubun to review since it's very important that we get benchmarking right.