Macro dipstick::mod_metrics

macro_rules! mod_metrics {
    ($type_param: ty, $metric_id: ident = ($($app_metrics: expr),+ $(,)*)) => { ... };
    ($type_param: ty, $metric_id: ident = [$($app_metrics: expr),+ $(,)*]) => { ... };
    ($type_param: ty, $metric_id: ident = $mod_metrics: expr) => { ... };
}

Define module-scoped metrics.