Runloop maintenance stage metrics (#2988)

# Description
Since the syncronized runloop mode was enabled, the maintenance task is
on the critical auction preparation path now, which takes some time. New
metrics should help finding the most expensive operations in order to
find a way to optimize them.
<img width="476" alt="image"
src="https://github.com/user-attachments/assets/921c7059-f5a9-493e-a71b-7af63cb479fd">

# Changes
A new HistogramVec metric with the `stage` label.

## How to test
Grafana.

crates/autopilot/src/maintenance.rs

@@ -18,10 +18,11 @@ use {
     futures::StreamExt,
     prometheus::{
         core::{AtomicU64, GenericGauge},
+        HistogramVec,
         IntCounterVec,
     },
     shared::maintenance::Maintaining,
-    std::{sync::Arc, time::Duration},
+    std::{future::Future, sync::Arc, time::Duration},
     tokio::{sync::Mutex, time::timeout},
 };
 
@@ -88,15 +89,21 @@ impl Maintenance {
     async fn update_inner(&self) -> Result<()> {
         // All these can run independently of each other.
         tokio::try_join!(
-            self.settlement_indexer.run_maintenance(),
-            self.db_cleanup.run_maintenance(),
-            self.index_ethflow_orders(),
-            futures::future::try_join_all(
-                self.cow_amm_indexer
-                    .iter()
-                    .cloned()
-                    .map(|indexer| async move { indexer.run_maintenance().await })
-            )
+            Self::timed_future(
+                "settlement_indexer",
+                self.settlement_indexer.run_maintenance()
+            ),
+            Self::timed_future("db_cleanup", self.db_cleanup.run_maintenance()),
+            Self::timed_future("ethflow_indexer", self.index_ethflow_orders()),
+            Self::timed_future(
+                "cow_amm_indexer",
+                futures::future::try_join_all(
+                    self.cow_amm_indexer
+                        .iter()
+                        .cloned()
+                        .map(|indexer| async move { indexer.run_maintenance().await }),
+                )
+            ),
         )?;
 
         Ok(())
@@ -170,6 +177,15 @@ impl Maintenance {
             }
         });
     }
+
+    /// Runs the future and collects runtime metrics.
+    async fn timed_future<T>(label: &str, fut: impl Future<Output = T>) -> T {
+        let _timer = metrics()
+            .maintenance_stage_time
+            .with_label_values(&[label])
+            .start_timer();
+        fut.await
+    }
 }
 
 type EthflowIndexer =
@@ -187,6 +203,13 @@ struct Metrics {
     /// Autopilot maintenance error counter
     #[metric(labels("result"))]
     updates: IntCounterVec,
+
+    /// Autopilot maintenance stage time
+    #[metric(
+        labels("stage"),
+        buckets(0.01, 0.05, 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2.0, 2.5, 3, 3.5, 4)
+    )]
+    maintenance_stage_time: HistogramVec,
 }
 
 fn metrics() -> &'static Metrics {