in src/metrics/meter.rs [63:72]
fn add_labels<K, V, I>(mut self, tags: I) -> Self
where
K: Into<String>,
V: Into<String>,
I: IntoIterator<Item = (K, V)>,
{
self.labels
.extend(tags.into_iter().map(|(k, v)| (k.into(), v.into())));
self
}