opt(lb): optimize the performance of weighted_random load balancer

Author: jizhuozhi

volo/src/discovery/mod.rs

@@ -165,8 +165,8 @@ impl Discover for StaticDiscover {
     }
 }
 
-/// [`WeightedStaticDiscover`] is a simple implementation of [`Discover`] that returns a static list of
-/// instances with weight.
+/// [`WeightedStaticDiscover`] is a simple implementation of [`Discover`] that returns a static list 
+/// of instances with weight.
 #[derive(Clone)]
 pub struct WeightedStaticDiscover {
     instances: Vec<Arc<Instance>>,

volo/src/loadbalance/random.rs

@@ -162,12 +162,16 @@ where
 
 #[cfg(test)]
 mod tests {
-    use super::{LoadBalance, WeightedRandomBalance};
-    use crate::discovery::WeightedStaticDiscover;
-    use crate::{context::Endpoint, discovery::StaticDiscover};
-    use rand::{rng, RngCore};
     use std::collections::HashMap;
 
+    use rand::{rng, RngCore};
+
+    use super::{LoadBalance, WeightedRandomBalance};
+    use crate::{
+        context::Endpoint,
+        discovery::{StaticDiscover, WeightedStaticDiscover},
+    };
+
     #[tokio::test]
     async fn test_weighted_random() {
         let empty = Endpoint::new("".into());