Clarify overflow comment in DelayDeactivation

Co-authored-by: ReubenBond <203839+ReubenBond@users.noreply.github.com>

Author: Copilot

src/Orleans.Runtime/Catalog/ActivationData.cs

@@ -482,7 +482,7 @@ public void DelayDeactivation(TimeSpan timespan)
     {
         if (timespan == TimeSpan.MaxValue || timespan == Timeout.InfiniteTimeSpan)
         {
-            // otherwise creates negative time.
+            // Adding these values to the current time would overflow, so use DateTime.MaxValue directly.
             KeepAliveUntil = DateTime.MaxValue;
         }
         else if (timespan <= TimeSpan.Zero)