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/samples/GettingStarted/Workflows/Checkpoint/CheckpointWithHumanInTheLoop/Program.cs

@@ -27,7 +27,7 @@ public static class Program
     private static async Task Main()
     {
         // Create the workflow
-        var workflow = await WorkflowHelper.GetWorkflowAsync();
+        var workflow = WorkflowHelper.GetWorkflow();
 
         // Create checkpoint manager
         var checkpointManager = CheckpointManager.Default;

dotnet/samples/GettingStarted/Workflows/Checkpoint/CheckpointWithHumanInTheLoop/WorkflowHelper.cs

@@ -10,7 +10,7 @@ internal static class WorkflowHelper
     /// Get a workflow that plays a number guessing game with human-in-the-loop interaction.
     /// An input port allows the external world to provide inputs to the workflow upon requests.
     /// </summary>
-    internal static ValueTask<Workflow<SignalWithNumber>> GetWorkflowAsync()
+    internal static Workflow GetWorkflow()
     {
         // Create the executors
         RequestPort numberRequest = RequestPort.Create<SignalWithNumber, int>("GuessNumber");
@@ -21,7 +21,7 @@ internal static class WorkflowHelper
             .AddEdge(numberRequest, judgeExecutor)
             .AddEdge(judgeExecutor, numberRequest)
             .WithOutputFrom(judgeExecutor)
-            .BuildAsync<SignalWithNumber>();
+            .Build();
     }
 }