HistogramCollector format cleanup (#15753)

## Description 

Describe the changes or additions included in this PR.

## Test Plan 

How did you test the new or updated feature?

---
If your changes are not user-facing and do not break anything, you can
skip the following section. Otherwise, please briefly describe what has
changed under the Release Notes section.

### Type of Change (Check all that apply)

- [ ] protocol change
- [ ] user-visible impact
- [ ] breaking change for a client SDKs
- [ ] breaking change for FNs (FN binary must upgrade)
- [ ] breaking change for validators or node operators (must upgrade
binaries)
- [ ] breaking change for on-chain data layout
- [ ] necessitate either a data wipe or data migration

### Release notes

crates/mysten-metrics/src/histogram.rs

@@ -224,9 +224,7 @@ impl HistogramCollector {
         const MAX_POINTS: usize = 500_000;
         loop {
             tokio::select! {
-             _ = &mut timeout => {
-                break;
-            },
+                _ = &mut timeout => break,
                 point = self.channel.recv() => {
                     count += 1;
                     if count > MAX_POINTS {
@@ -239,8 +237,8 @@ impl HistogramCollector {
                         // Histogram no longer exists
                         return Err(());
                     }
-                }
-                }
+                },
+            }
         }
         if count > MAX_POINTS {
             error!(