proxy: format imports with nightly rustfmt (#9414)

```shell
cargo +nightly fmt -p proxy -- -l --config imports_granularity=Module,group_imports=StdExternalCrate,reorder_imports=true
```

These rust-analyzer settings for VSCode should help retain this style:
```json
  "rust-analyzer.imports.group.enable": true,
  "rust-analyzer.imports.prefix": "crate",
  "rust-analyzer.imports.merge.glob": false,
  "rust-analyzer.imports.granularity.group": "module",
  "rust-analyzer.imports.granularity.enforce": true,
```

proxy/src/rate_limiter/limit_algorithm/aimd.rs

@@ -60,12 +60,11 @@ impl LimitAlgorithm for Aimd {
 mod tests {
     use std::time::Duration;
 
+    use super::*;
     use crate::rate_limiter::limit_algorithm::{
         DynamicLimiter, RateLimitAlgorithm, RateLimiterConfig,
     };
 
-    use super::*;
-
     #[tokio::test(start_paused = true)]
     async fn increase_decrease() {
         let config = RateLimiterConfig {