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/waiters.rs

@@ -1,8 +1,9 @@
+use std::pin::Pin;
+use std::task;
+
 use hashbrown::HashMap;
 use parking_lot::Mutex;
 use pin_project_lite::pin_project;
-use std::pin::Pin;
-use std::task;
 use thiserror::Error;
 use tokio::sync::oneshot;
 
@@ -99,9 +100,10 @@ impl<T> std::future::Future for Waiter<'_, T> {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use std::sync::Arc;
 
+    use super::*;
+
     #[tokio::test]
     async fn test_waiter() -> anyhow::Result<()> {
         let waiters = Arc::new(Waiters::default());