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/sasl/messages.rs

@@ -1,8 +1,9 @@
 //! Definitions for SASL messages.
 
-use crate::parse::{split_at_const, split_cstr};
 use pq_proto::{BeAuthenticationSaslMessage, BeMessage};
 
+use crate::parse::{split_at_const, split_cstr};
+
 /// SASL-specific payload of [`PasswordMessage`](pq_proto::FeMessage::PasswordMessage).
 #[derive(Debug)]
 pub(crate) struct FirstMessage<'a> {

proxy/src/sasl/mod.rs

@@ -10,13 +10,14 @@ mod channel_binding;
 mod messages;
 mod stream;
 
-use crate::error::{ReportableError, UserFacingError};
 use std::io;
-use thiserror::Error;
 
 pub(crate) use channel_binding::ChannelBinding;
 pub(crate) use messages::FirstMessage;
 pub(crate) use stream::{Outcome, SaslStream};
+use thiserror::Error;
+
+use crate::error::{ReportableError, UserFacingError};
 
 /// Fine-grained auth errors help in writing tests.
 #[derive(Error, Debug)]

proxy/src/sasl/stream.rs

@@ -1,11 +1,14 @@
 //! Abstraction for the string-oriented SASL protocols.
 
-use super::{messages::ServerMessage, Mechanism};
-use crate::stream::PqStream;
 use std::io;
+
 use tokio::io::{AsyncRead, AsyncWrite};
 use tracing::info;
 
+use super::messages::ServerMessage;
+use super::Mechanism;
+use crate::stream::PqStream;
+
 /// Abstracts away all peculiarities of the libpq's protocol.
 pub(crate) struct SaslStream<'a, S> {
     /// The underlying stream.