Make ProcessMessages synchronous now that it no longer awaits

The dedup branch no longer awaits _messageClearer.Clear (it stages the
position and persists it to the DeliveredPositionsId effect instead), so
ProcessMessages has no remaining awaits. Change it from async Task to void
and drop the await at both call sites (Push, FetchAndNotify). Both callers
remain async for the fetch semaphore and message-store calls.

Author: stidsborg

Core/Cleipnir.ResilientFunctions/Queuing/QueueManager.cs

@@ -136,7 +136,7 @@ public async Task Push(IReadOnlyList<StoredMessage> messages)
             if (_thrownException != null)
                 return;
 
-            await ProcessMessages(messages);
+            ProcessMessages(messages);
         }
         finally
         {
@@ -200,7 +200,7 @@ private async Task FetchAndNotify()
                 skipPositions = _fetchedPositions.ToList();
 
             var messages = await _messageStore.GetMessages(_storedId, skipPositions);
-            await ProcessMessages(messages);
+            ProcessMessages(messages);
         }
         finally
         {
@@ -211,7 +211,7 @@ private async Task FetchAndNotify()
 
     // Caller must hold _fetchSemaphore. Deserializes, dedups by idempotency-key and by already-fetched
     // position (so pushes are idempotent), and stages messages for delivery.
-    private async Task ProcessMessages(IReadOnlyList<StoredMessage> messages)
+    private void ProcessMessages(IReadOnlyList<StoredMessage> messages)
     {
         foreach (var (messageContent, messageType, position, _, idempotencyKey, sender, receiver) in messages)
         {