refactor: [BREAKING] Remove generic Workflow<T> (#1551)

Remove input type checking in favour of explicit `.DescribeProtocolAsync()` flow. Also removes `.AsAgentAsync()` as the validation happens at workflow run time. This makes it easier to use Workflows with DI without resorting to async-over-sync.

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

@@ -0,0 +1,23 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.Agents.AI.Workflows;
+
+/// <summary>
+/// Describes the protocol for communication with a <see cref="Workflow"/> or <see cref="Executor"/>.
+/// </summary>
+public class ProtocolDescriptor
+{
+    /// <summary>
+    /// Get the collection of types accepted by the <see cref="Workflow"/> or <see cref="Executor"/>.
+    /// </summary>
+    public IEnumerable<Type> Accepts { get; }
+
+    internal ProtocolDescriptor(IEnumerable<Type> acceptedTypes)
+    {
+        this.Accepts = acceptedTypes.ToArray();
+    }
+}