serialization fixing world unit test and missing serialize for inert.

Game/Entity/EntityManager.cpp

@@ -140,4 +140,6 @@ Entity* deserialize_entity(Archive& ar, EntityManager& manager)
     }
 
     entity_base->is_dirty = false;
+
+    return entity_base;
 }

Game/Entity/entity_types.cpp

@@ -1,4 +1,9 @@
 #include <Entity/entity_types.h>
 
+#include <Core/Common/serialization.h>
+
 DEFINE_ENTITY_VERSIONED(Inert, 1)
-internal void serialize(Archive& /*ar*/, uint16 /*version*/, Inert& /*inert*/) {}
+internal void serialize(Archive& ar, uint16 /*version*/, Inert& inert) 
+{
+    SERIALIZE(ar, MeshInstance, inert.MeshInstance);
+}