Function observer_new

pub fn observer_new<D, M, S>(
    m: MetricsCollection,
    get_single: S,
    get_multi: M,
    shared: D,
) -> impl FnMut(&Context)
where
    S: FnMut(&mut D, &str) -> Option<Row>,
    M: FnMut(&mut D, &str) -> Vec<Row>,

Creates new observer.