Feature request: profile benchmarking "mode"

[RossComputerGuy]

I'm looking for a way to effectively benchmark my libxev event loops per iteration of the loop. It may be possible to write libxev to have a comptime enabled "profiling mode" which measures the speed of each completion and each iteration of the loop. The benefit of doing this in libxev would be that it's standard and doesn't rely on some trickery. The only real issue I see here is determining what measurement should be used. Maybe it's possible to set different ones through an enum, some options could possibly be real_time, cpu_time, etc. It should also be possible to hook into some sort of method to retrieve the data so it may be logged by the developer.