Function monitored_scope

pub fn monitored_scope(name: &'static str) -> Option<MonitoredScopeGuard>

This function creates a named scoped object, that keeps track of

• the total iterations where the scope is called in the monitored_scope_iterations metric.
• and the total duration of the scope in the monitored_scope_duration_ns metric.

The monitored scope should be single threaded, e.g. the scoped object encompass the lifetime of a select loop or guarded by mutex. Then the rate of monitored_scope_duration_ns, converted to the unit of sec / sec, would be how full the single threaded scope is running.