Observability wrappers for photon-ring channels.

Provides framework-agnostic metric snapshots from photon-ring's built-in counters (total_received, total_lagged, receive_ratio, published, pending).

Example

use photon_ring_metrics::SubscriberMetrics;

let (mut pub_, subs) = photon_ring::channel::<u64>(1024);
let mut sub = subs.subscribe();
let metrics = SubscriberMetrics::new(&sub);

pub_.publish(42);
sub.try_recv().unwrap();

let snapshot = metrics.snapshot(&sub);
assert_eq!(snapshot.total_received, 1);
assert_eq!(snapshot.total_lagged, 0);