fix some existing issues

LightlessSync/Utils/RollingList.cs

@@ -29,6 +29,29 @@ public class RollingList<T> : IEnumerable<T>
         }
     }
 
+    public bool TryGetLast(out T value)
+    {
+        lock (_addLock)
+        {
+            if (_list.Count == 0)
+            {
+                value = default!;
+                return false;
+            }
+
+            value = _list.Last!.Value;
+            return true;
+        }
+    }
+
+    public List<T> Snapshot()
+    {
+        lock (_addLock)
+        {
+            return new List<T>(_list);
+        }
+    }
+
     public void Add(T value)
     {
         lock (_addLock)