restructure includes in error.hpp

benchmarks/error.hpp

@@ -1,6 +1,9 @@
-#include <dml/dml.hpp>
+#pragma once
+
 #include <iostream>
 
+#include <dml/dml.hpp>
+
 inline std::ostream& operator<<(std::ostream& strm, const dml::status_code code) {
     switch(code) {
         case dml::status_code::ok: strm << "[ok]"; break;