chore(proxy): use specially named prepared statements for type-checking (#10843)

I was looking into
https://github.com/neondatabase/serverless/issues/144, I recall previous
cases where proxy would trigger these prepared statements which would
conflict with other statements prepared by our client downstream.

Because of that, and also to aid in debugging, I've made sure all
prepared statements that proxy needs to make have specific names that
likely won't conflict and makes it clear in a error log if it's our
statements that are causing issues

proxy/src/serverless/backend.rs

@@ -372,7 +372,7 @@ impl PoolingBackend {
             debug!("setting up backend session state");
 
             // initiates the auth session
-            if let Err(e) = client.execute("select auth.init()", &[]).await {
+            if let Err(e) = client.batch_execute("select auth.init();").await {
                 discard.discard();
                 return Err(e.into());
             }

proxy/src/serverless/local_conn_pool.rs

@@ -23,7 +23,6 @@ use indexmap::IndexMap;
 use jose_jwk::jose_b64::base64ct::{Base64UrlUnpadded, Encoding};
 use parking_lot::RwLock;
 use postgres_client::tls::NoTlsStream;
-use postgres_client::types::ToSql;
 use postgres_client::AsyncMessage;
 use serde_json::value::RawValue;
 use tokio::net::TcpStream;
@@ -281,13 +280,9 @@ impl ClientInnerCommon<postgres_client::Client> {
             let token = resign_jwt(&local_data.key, payload, local_data.jti)?;
 
             // initiates the auth session
-            self.inner.batch_execute("discard all").await?;
-            self.inner
-                .execute(
-                    "select auth.jwt_session_init($1)",
-                    &[&&*token as &(dyn ToSql + Sync)],
-                )
-                .await?;
+            // this is safe from query injections as the jwt format free of any escape characters.
+            let query = format!("discard all; select auth.jwt_session_init('{token}')");
+            self.inner.batch_execute(&query).await?;
 
             let pid = self.inner.get_process_id();
             info!(pid, jti = local_data.jti, "user session state init");