fix: Changes Map.Sector.Items to link list. (#1547)

### Summary

Eliminates `IPooledEnumerable<T>` and `eable.Free()` from `Map` for items. This drastically simplifies code that iterates in range, for example:

```cs
foreach (var item in m.GetItemsInRange(5))
{
}
```
The code above no longer requires an eable and calling `Free()`.

Projects/UOContent/Items/Containers/MarkContainer.cs

@@ -130,15 +130,14 @@ public partial class MarkContainer : LockableContainer
 
     private static bool FindMarkContainer(Point3D p, Map map)
     {
-        var eable = map.GetItemsInRange<MarkContainer>(p, 0);
-
-        foreach (var item in eable)
+        foreach (var item in map.GetItemsInRange<MarkContainer>(p, 0))
         {
             if (item.Z == p.Z)
             {
                 return true;
             }
         }
+
         return false;
     }