fix(mysql): initialize transaction query timing

crates/dbx-drivers/src/db/mysql.rs

@@ -5350,6 +5350,7 @@ pub async fn execute_transaction_statement_on_conn(
             rows: Vec::new(),
             affected_rows,
             execution_time_ms: started_at.elapsed().as_millis(),
+            server_execute_time_us: None,
             truncated: false,
             session_id: None,
             has_more: false,
@@ -5383,6 +5384,7 @@ pub async fn execute_transaction_statement_on_conn(
             rows,
             affected_rows: 0,
             execution_time_ms: started_at.elapsed().as_millis(),
+            server_execute_time_us: None,
             truncated,
             session_id: None,
             has_more: false,