Provide a way to set the interval for samples when profiling about viceroy HOT 1 OPEN

I'm in favor of this suggestion. There's a subtlety though, which is that the EPOCH_INTERRUPTION_PERIOD is used regardless of whether the guest profiler is enabled or not. It also has an impact on how long the guest can run before async background tasks get an opportunity to make progress. As I recall, Rainy and I had some trouble with Viceroy's test suite unless we set the interval fairly short.

It's probably worth putting some thought into what the default interval should be in both cases: 10ms for Wasmtime and 50µs for Viceroy are both pretty arbitrary choices. It makes some sense that they're different if we assume that Viceroy guests are usually short-lived compared with Wasmtime guests, but the exact durations are still not well justified.

One Viceroy user reported a cost I hadn't considered of having a short interval: There's a thread that wakes up briefly on that interval, even if no guests are running at the time, and that prevents the CPU from going into deeper power-saving states. So Viceroy users on battery might need a longer interval for power management reasons. Eventually it'd be nice to pause the epoch-interruption thread while there are no requests in flight, but that's some extra complexity.

from viceroy.