Replay pending deletions on QueueManager.Initialize (#151)

DeliveredPositionsId was migrated in d8fefad from a parent-with-children
layout to a single List<long> value, but Initialize still scanned for
children — which no writer produces anymore. Restarted flows therefore
never replayed pending message deletions.

Read the persisted List<long> directly, matching the AfterFlush write
pattern.

Author: stidsborg

Core/Cleipnir.ResilientFunctions/Queuing/QueueManager.cs

@@ -83,19 +83,11 @@ private async Task Initialize()
 
             _idempotencyKeys.Initialize();
 
-            var children = _effect.GetChildren(DeliveredPositionsId);
-            var positions = new List<long>();
-            foreach (var childId in children)
-            {
-                var position = _effect.Get<long>(childId);
-                positions.Add(position);
-            }
-
-            if (positions.Any())
+            if (_effect.TryGet<List<long>>(DeliveredPositionsId, out var positions) && positions is { Count: > 0 })
             {
                 await _messageStore.DeleteMessages(_storedId, positions);
-                foreach (var childId in children)
-                    await _effect.Clear(childId, flush: false);
+                positions.Clear();
+                _effect.FlushlessUpsert(DeliveredPositionsId, positions, alias: null);
             }
 
             _initialized = true;