fix: Adds GetClients to map iterators (#1574)

### Summary

Eliminates `IPooledEnumerable<NetState>` and `eable.Free()` from `Map` for clients. This drastically simplifies code that iterates in range, for example:

```cs
foreach (var m in m.GetClientsInRange(5))
{
}
```
The code above no longer requires an eable and calling `Free()`.

Projects/Server/Maps/Map.MobileEnumerator.cs

@@ -84,8 +84,8 @@ public partial class Map
             get => new();
         }
 
-        private Map _map;
-        private Point2D _location;
+        private readonly Map _map;
+        private readonly Point2D _location;
 
         public MobileAtEnumerable(Map map, Point2D loc)
         {