Macro product_metrics 

macro_rules! product_metrics {
    ($(#[$meta:meta])* $vis:vis struct $name:ident {
        $($(#[$field_meta:meta])* $field:ident : $kind:ident ($($args:expr),* $(,)? ) $(.with_unit($unit:expr))?),* $(,)?
    }) => { ... };
    (@type counter) => { ... };
    (@type gauge) => { ... };
    (@type histogram) => { ... };
    (@type histogram_with_buckets) => { ... };
}

Declare one typed schema and register it atomically against an explicit provider.