Add notes regarding using inline delegates with Scheduler.AddOnce

osu.Framework.Tests/Threading/SchedulerTest.cs

@@ -429,6 +429,8 @@ namespace osu.Framework.Tests.Threading
         {
             classInvocations = 0;
 
+            // Note that while this works here (even with a capture), there's no guarantee that will always be the
+            // case. As such it's always best to use a local function or private method.
             for (int i = 0; i < 10; i++)
                 invokeInlineDelegateAction();
 

osu.Framework/Threading/Scheduler.cs

@@ -368,7 +368,7 @@ namespace osu.Framework.Threading
         /// Adds a task which will only be run once per frame, no matter how many times it was scheduled in the previous frame.
         /// </summary>
         /// <remarks>The task will be run on the next <see cref="Update"/> independent of the current clock time.</remarks>
-        /// <param name="task">The work to be done.</param>
+        /// <param name="task">The work to be done. Avoid using inline delegates as they may not be cached, bypassing the once-per-frame guarantee.</param>
         /// <returns>Whether this is the first queue attempt of this work.</returns>
         public bool AddOnce(Action task)
         {