refactor: simplify iterator usage and improve command execution

- Replace manual `while (iter.MoveNext())` loops with `foreach` loops in
  tests
- Implement batching and mutation flushing in `CommandQueue.ExecuteAll`
  to
  ensure chained commands see each other's changes

OECS/CommandQueue.cs

@@ -41,11 +41,18 @@ public class CommandQueue
     /// <summary>
     /// Executes all queued commands in FIFO order against the given world.
     ///
+    /// Commands run inside a batching scope — structural mutations are
+    /// deferred and <see cref="World.GetComponent{T}"/> calls are
+    /// auto-tracked for modification until the drain completes.
+    /// Pending mutations are flushed after each command, so chained
+    /// commands see each other's changes within the same drain cycle.
+    ///
     /// The queue is fully drained — commands enqueued by other commands during
     /// this call are also executed before the method returns.
     /// </summary>
     public void ExecuteAll(World world)
     {
+        world.BeginBatching();
         int index = 0;
         while (index < _commands.Count)
         {
@@ -60,9 +67,13 @@ public class CommandQueue
             {
                 _errors.Add(ex);
             }
+
+            // Flush after each command so chained commands see mutations.
+            world.FlushPendingMutations();
         }
 
         _commands.Clear();
+        world.EndBatching();
     }
 
     /// <summary>