common/concepts: Move <type_traits> include out of the Common namespace

This is a compiler/linker error waiting to happen.

src/common/concepts.h

@@ -4,10 +4,10 @@
 
 #pragma once
 
-namespace Common {
-
 #include <type_traits>
 
+namespace Common {
+
 // Check if type is like an STL container
 template <typename T>
 concept IsSTLContainer = requires(T t) {