only register if any tasks to register

Author: YunchuWang

src/Generators/DurableTaskSourceGenerator.cs

@@ -358,11 +358,15 @@ public static class GeneratedDurableTaskExtensions
             else
             {
                 // ASP.NET Core-specific service registration methods
-                AddRegistrationMethodForAllTasks(
-                    sourceBuilder,
-                    orchestrators,
-                    activities,
-                    entities);
+                // Only generate if there are actually tasks to register
+                if (orchestrators.Count > 0 || activities.Count > 0 || entities.Count > 0)
+                {
+                    AddRegistrationMethodForAllTasks(
+                        sourceBuilder,
+                        orchestrators,
+                        activities,
+                        entities);   
+                }
             }
 
             sourceBuilder.AppendLine("    }").AppendLine("}");