proxy refactor large files (#6153)

## Problem

The `src/proxy.rs` file is far too large

## Summary of changes

Creates 3 new files:
```
src/metrics.rs
src/proxy/retry.rs
src/proxy/connect_compute.rs
```

proxy/src/auth/backend.rs

@@ -11,7 +11,8 @@ use crate::auth::validate_password_and_exchange;
 use crate::console::errors::GetAuthInfoError;
 use crate::console::provider::AuthInfo;
 use crate::console::AuthSecret;
-use crate::proxy::{handle_try_wake, retry_after, LatencyTimer};
+use crate::proxy::connect_compute::handle_try_wake;
+use crate::proxy::retry::retry_after;
 use crate::scram;
 use crate::stream::Stream;
 use crate::{
@@ -22,6 +23,7 @@ use crate::{
         provider::{CachedNodeInfo, ConsoleReqExtra},
         Api,
     },
+    metrics::LatencyTimer,
     stream, url,
 };
 use futures::TryFutureExt;

proxy/src/auth/backend/classic.rs

@@ -4,7 +4,7 @@ use crate::{
     compute,
     config::AuthenticationConfig,
     console::AuthSecret,
-    proxy::LatencyTimer,
+    metrics::LatencyTimer,
     sasl,
     stream::{PqStream, Stream},
 };

proxy/src/auth/backend/hacks.rs

@@ -4,7 +4,7 @@ use super::{
 use crate::{
     auth::{self, AuthFlow},
     console::AuthSecret,
-    proxy::LatencyTimer,
+    metrics::LatencyTimer,
     sasl,
     stream::{self, Stream},
 };

proxy/src/auth/credentials.rs

@@ -1,9 +1,8 @@
 //! User credentials used in authentication.
 
 use crate::{
-    auth::password_hack::parse_endpoint_param,
-    error::UserFacingError,
-    proxy::{neon_options_str, NUM_CONNECTION_ACCEPTED_BY_SNI},
+    auth::password_hack::parse_endpoint_param, error::UserFacingError,
+    metrics::NUM_CONNECTION_ACCEPTED_BY_SNI, proxy::neon_options_str,
 };
 use itertools::Itertools;
 use pq_proto::StartupMessageParams;