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/serverless/sql_over_http.rs

@@ -182,16 +182,16 @@ fn get_conn_info(
 
     for (key, value) in pairs {
         if key == "options" {
-            options = Some(value.to_string());
+            options = Some(value.into());
             break;
         }
     }
 
     Ok(ConnInfo {
-        username: username.to_owned(),
-        dbname: dbname.to_owned(),
-        hostname: hostname.to_owned(),
-        password: password.to_owned(),
+        username: username.into(),
+        dbname: dbname.into(),
+        hostname: hostname.into(),
+        password: password.into(),
         options,
     })
 }