pub fn start(self) -> BenchmarkTimerGuard {
        BenchmarkTimerGuard {
            started_at: Instant::now(),
            observation: self.observation,
        }
    }
Starts the timer. The timer will remain active until the returned guard is dropped. If you drop the timer implicitly,
be careful with the drop order (inverse to the variable declaration order); when in doubt, drop the guard explicitly.
core/tests/vm-benchmark/src/criterion.rs