Core/WorldObject: Replace non-std::chrono SummonGameObject overloads

Also fix intended despawn time of GOs used by the "Engineering a Disaster" quest

(cherry picked from commit 8642aaaf9268364454b409db7eb62f31210e6d6c)

src/server/scripts/Commands/cs_gobject.cpp

@@ -202,10 +202,10 @@ public:
         Player* player = handler->GetSession()->GetPlayer();
 
         char* spawntime = strtok(nullptr, " ");
-        uint32 spawntm = 300;
+        Seconds spawntm = 300s;
 
         if (spawntime)
-            spawntm = atoul(spawntime);
+            spawntm = Seconds(atoul(spawntime));
 
         uint32 objectId = atoul(id);