Rename WorkflowOutputEvent.SourceId to ExecutorId for Python consistency

- Rename SourceId property to ExecutorId in WorkflowOutputEvent
- Add [Obsolete] SourceId property for backward compatibility
- Update all test usages to use ExecutorId

Resolves part of #2938

Author: lokitoth

dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowOutputEvent.cs

@@ -10,15 +10,21 @@ namespace Microsoft.Agents.AI.Workflows;
 /// </summary>
 public sealed class WorkflowOutputEvent : WorkflowEvent
 {
-    internal WorkflowOutputEvent(object data, string sourceId) : base(data)
+    internal WorkflowOutputEvent(object data, string executorId) : base(data)
     {
-        this.SourceId = sourceId;
+        this.ExecutorId = executorId;
     }
 
     /// <summary>
     /// The unique identifier of the executor that yielded this output.
     /// </summary>
-    public string SourceId { get; }
+    public string ExecutorId { get; }
+
+    /// <summary>
+    /// The unique identifier of the executor that yielded this output.
+    /// </summary>
+    [Obsolete("Use ExecutorId instead.")]
+    public string SourceId => this.ExecutorId;
 
     /// <summary>
     /// Determines whether the underlying data is of the specified type or a derived type.

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/Sample/04_Simple_Workflow_ExternalRequest.cs

@@ -45,7 +45,7 @@ public static async ValueTask<string> RunAsync(TextWriter writer, Func<string, i
             switch (evt)
             {
                 case WorkflowOutputEvent outputEvent:
-                    switch (outputEvent.SourceId)
+                    switch (outputEvent.ExecutorId)
                     {
                         case JudgeId:
                             if (outputEvent.Is(out NumberSignal newSignal))

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/Sample/05_Simple_Workflow_Checkpointing.cs

@@ -79,7 +79,7 @@ await environment.StreamAsync(workflow, NumberSignal.Init, checkpointManager)
                 switch (evt)
                 {
                     case WorkflowOutputEvent outputEvent:
-                        switch (outputEvent.SourceId)
+                        switch (outputEvent.ExecutorId)
                         {
                             case Step4EntryPoint.JudgeId:
                                 if (outputEvent.Is(out NumberSignal newSignal))

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/Sample/13_Subworkflow_Checkpointing.cs

@@ -64,7 +64,7 @@ public static async ValueTask<CheckpointInfo> RunAsync(TextWriter writer, string
                 {
                     foreach (ChatMessage message in messages)
                     {
-                        writer.WriteLine($"{output.SourceId}: {message.Text}");
+                        writer.WriteLine($"{output.ExecutorId}: {message.Text}");
                     }
                 }
                 else