Fixes for XA transactions with streaming enabled

Changes mostly related to handling of XA PREPARE fragments

dbsim/db_client_service.hpp

@@ -48,6 +48,10 @@ namespace db
         {
             return false;
         }
+        bool is_xa_prepare () const override
+        {
+            return false;
+        }
         size_t bytes_generated() const override
         {
             return 0;