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/Spawners/Commands/GenerateSpawnersCommand.cs

@@ -147,8 +147,7 @@ namespace Server.Engines.Spawners
 
                 // Delete all spawners at this location.
                 // Probably shouldn't do this outside of migrations? Is there a better way to find/fix spawners?
-                var eable = map.GetItemsInRange<BaseSpawner>(location, 0);
-                foreach (var spawner in eable)
+                foreach (var spawner in map.GetItemsInRange<BaseSpawner>(location, 0))
                 {
                     if (spawner.GetType() == type)
                     {