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/BaseCreature.cs

@@ -3638,9 +3638,8 @@ namespace Server.Mobiles
                 return false;
             }
 
-            var eable = GetItemsInRange<Corpse>(2);
             Corpse toRummage = null;
-            foreach (var c in eable)
+            foreach (var c in GetItemsInRange<Corpse>(2))
             {
                 if (c.Items.Count > 0)
                 {