sightglass-next: extract native baseline benchmarking from webui_runner

One useful feature of the original sightglass code was the ability to run the benchmarks as native machine code in order to form a baseline for comparison. If we migrate this functionality from `webui_runner` to `benchmarks-next` (e.g.), we can then fully replace the old sightglass runner with the new one.

This involves some investigation to determine how to hook into the `bench_start()` and `bench_end()` calls with `perf`.