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/Server/Regions/Region.cs

@@ -295,15 +295,15 @@ public class Region : IComparable<Region>, IValueLinkListNode<Region>
         }
 
         var sector = map.GetSector(p);
-        var list = sector.RegionRects;
+        var list = sector.Regions;
 
         for (var i = 0; i < list.Count; ++i)
         {
-            var regRect = list[i];
+            var region = list[i];
 
-            if (regRect.Contains(p))
+            if (region.Contains(p))
             {
-                return regRect.Region;
+                return region;
             }
         }