proxy: chore: replace strings with SmolStr (#5786)

## Problem

no problem

## Summary of changes

replaces boxstr with arcstr as it's cheaper to clone. mild perf
improvement.

probably should look into other smallstring optimsations tbh, they will
likely be even better. The longest endpoint name I was able to construct
is something like `ep-weathered-wildflower-12345678` which is 32 bytes.
Most string optimisations top out at 23 bytes

proxy/src/console/messages.rs

@@ -1,4 +1,5 @@
 use serde::Deserialize;
+use smol_str::SmolStr;
 use std::fmt;
 
 /// Generic error response with human-readable description.
@@ -88,11 +89,11 @@ impl fmt::Debug for DatabaseInfo {
 
 /// Various labels for prometheus metrics.
 /// Also known as `ProxyMetricsAuxInfo` in the console.
-#[derive(Debug, Deserialize, Default)]
+#[derive(Debug, Deserialize, Clone, Default)]
 pub struct MetricsAuxInfo {
-    pub endpoint_id: Box<str>,
-    pub project_id: Box<str>,
-    pub branch_id: Box<str>,
+    pub endpoint_id: SmolStr,
+    pub project_id: SmolStr,
+    pub branch_id: SmolStr,
 }
 
 impl MetricsAuxInfo {

proxy/src/console/provider.rs

@@ -229,7 +229,7 @@ pub struct NodeInfo {
     pub config: compute::ConnCfg,
 
     /// Labels for proxy's metrics.
-    pub aux: Arc<MetricsAuxInfo>,
+    pub aux: MetricsAuxInfo,
 
     /// Whether we should accept self-signed certificates (for testing)
     pub allow_self_signed_compute: bool,

proxy/src/console/provider/neon.rs

@@ -144,7 +144,7 @@ impl Api {
 
             let node = NodeInfo {
                 config,
-                aux: body.aux.into(),
+                aux: body.aux,
                 allow_self_signed_compute: false,
             };