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/Mobiles/AI/BaseAI.cs

@@ -2157,10 +2157,7 @@ public abstract class BaseAI
                 Movement.Movement.Offset(d, ref x, ref y);
 
                 var destroyables = 0;
-
-                var eable = map.GetItemsInRange(new Point3D(x, y, m_Mobile.Location.Z), 1);
-
-                foreach (var item in eable)
+                foreach (var item in map.GetItemsInRange(new Point3D(x, y, m_Mobile.Location.Z), 1))
                 {
                     if (canOpenDoors && item is BaseDoor door && door.Z + door.ItemData.Height > m_Mobile.Z &&
                         m_Mobile.Z + 16 > door.Z)