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/Engines/Harvest/Core/HarvestSystem.cs

@@ -307,8 +307,7 @@ namespace Server.Engines.Harvest
                 return false;
             }
 
-            var eable = m.GetItemsInRange(0);
-            foreach (var i in eable)
+            foreach (var i in m.GetItemsInRange(0))
             {
                 if (i.StackWith(m, i, false))
                 {