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/Spells/Third/Teleport.cs

@@ -96,9 +96,7 @@ namespace Server.Spells.Third
 
                 m.PlaySound(0x1FE);
 
-                var eable = m.GetItemsInRange(0);
-
-                foreach (var item in eable)
+                foreach (var item in m.GetItemsInRange(0))
                 {
                     if (item is ParalyzeFieldSpell.InternalItem or
                         PoisonFieldSpell.InternalItem or FireFieldSpell.FireFieldItem)