.NET: [BREAKING] Enable sharing of workflow instances across concurrently executing runs (#1464)

* refactor: remove unused internals

* feat: Execution Mode for sharing a workflow among concurrent runs

* feat: Update WorkflowHostAgent to support concurrent execution

* Also update AsAgent APIs to support injecting a CheckpointManager and an IWorkflowExecutionEnvironment

* fix: Make Read logic consistent in DeclarativeWorkflowContext

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

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Agents.AI.Workflows;
 
@@ -26,6 +27,24 @@ public sealed class WorkflowOutputEvent : WorkflowEvent
     /// <returns>true if the underlying data is assignable to type T; otherwise, false.</returns>
     public bool Is<T>() => this.IsType(typeof(T));
 
+    /// <summary>
+    /// Determines whether the underlying data is of the specified type or a derived type, and
+    /// returns it as that type if it is.
+    /// </summary>
+    /// <typeparam name="T">The type to compare with the type of the underlying data.</typeparam>
+    /// <returns>true if the underlying data is assignable to type T; otherwise, false.</returns>
+    public bool Is<T>([NotNullWhen(true)] out T? maybeValue)
+    {
+        if (this.Data is T value)
+        {
+            maybeValue = value;
+            return true;
+        }
+
+        maybeValue = default;
+        return false;
+    }
+
     /// <summary>
     /// Determines whether the underlying data is of the specified type or a derived type.
     /// </summary>