refactor: simplify NATS metrics scraping interval logic

- Remove INITIAL_WAIT_MS constant and exponential backoff
- Use fixed 9.8s interval (MAX_WAIT_MS) for all scrapes
- Perform first scrape immediately for faster metrics availability
- Inline NATS timeout constant (500ms)
- Update tests to use 500ms waits since metrics are available immediately

Signed-off-by: Keiven Chang <keivenchang@users.noreply.github.com>

Author: keivenchang

lib/runtime/src/component.rs

@@ -273,13 +273,12 @@ impl Component {
     /// Add Prometheus metrics for this component's NATS service stats.
     ///
     /// Starts a background task that periodically requests service statistics from NATS
-    /// and updates the corresponding Prometheus metrics. The scraping interval starts at
-    /// 500ms (INITIAL_WAIT_MS) and doubles after each scrape (regardless of success or failure)
-    /// up to 9.8 seconds (MAX_WAIT_MS).
+    /// and updates the corresponding Prometheus metrics. The first scrape happens immediately,
+    /// then subsequent scrapes occur at a fixed interval of 9.8 seconds (MAX_WAIT_MS),
+    /// which should be near or smaller than typical Prometheus scraping intervals to ensure
+    /// metrics are fresh when Prometheus collects them.
     pub fn start_scraping_nats_service_component_metrics(&self) -> Result<()> {
-        const NATS_TIMEOUT_MS: std::time::Duration = std::time::Duration::from_millis(300);
-        const INITIAL_WAIT_MS: std::time::Duration = std::time::Duration::from_millis(500);
-        const MAX_WAIT_MS: std::time::Duration = std::time::Duration::from_millis(9800); // Arbitrary value
+        const MAX_WAIT_MS: std::time::Duration = std::time::Duration::from_millis(9800); // Should be <= Prometheus scrape interval
 
         // If there is another component with the same service name, this will fail.
         let component_metrics = ComponentNatsServerPrometheusMetrics::new(self)?;
@@ -308,9 +307,8 @@ impl Component {
         // By using the DRT's own runtime handle, we ensure the task runs in the
         // correct runtime that will persist for the lifetime of the component.
         c.drt().runtime().secondary().spawn(async move {
-            let timeout = NATS_TIMEOUT_MS;
-            let mut current_wait = INITIAL_WAIT_MS;
-            let mut interval = tokio::time::interval(current_wait);
+            let timeout = std::time::Duration::from_millis(500);
+            let mut interval = tokio::time::interval(MAX_WAIT_MS);
             interval.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Skip);
 
             loop {
@@ -328,14 +326,6 @@ impl Component {
                     }
                 }
 
-                // Always double the wait time up to MAX_WAIT_MS
-                let new_wait = std::cmp::min(current_wait * 2, MAX_WAIT_MS);
-                if new_wait != current_wait {
-                    current_wait = new_wait;
-                    interval = tokio::time::interval(current_wait);
-                    interval.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Skip);
-                }
-
                 interval.tick().await;
             }
         });

lib/runtime/src/metrics.rs

@@ -1527,6 +1527,10 @@ mod test_metricsregistry_nats {
         }
         println!("✓ Sent messages and received responses successfully");
 
+        println!("\n=== Waiting 500ms for metrics to update ===");
+        sleep(Duration::from_millis(500)).await;
+        println!("✓ Wait complete, getting final metrics...");
+
         let final_drt_output = drt.prometheus_metrics_fmt().unwrap();
         println!("\n=== Final Prometheus DRT output ===");
         println!("{}", final_drt_output);
@@ -1542,10 +1546,6 @@ mod test_metricsregistry_nats {
             .filter_map(|line| super::test_helpers::parse_prometheus_metric(line.as_str()))
             .collect();
 
-        println!("\n=== Waiting 1 second for metrics to stabilize ===");
-        sleep(Duration::from_secs(1)).await;
-        println!("✓ Wait complete, checking final metrics...");
-
         let post_expected_metric_values = [
             // DRT NATS metrics
             (