Python: .NET: Executor source gen for workflow executor routing (#3131)

* Roslyn Source Generators for Workflow Executor Routing.

* Update dotnet/src/Microsoft.Agents.AI.Workflows.Generators/ExecutorRouteGenerator.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* WIP.

* All fixed up except dangling sends/yields attriutes, working on that next.

* Add protocol-only generation for SendsMessage/YieldsOutput attributes

* Ensuring collections that can change order are sorted to enable pipeline caching.

* Improvents per PR feedback.

---------

Co-authored-by: alliscode <bentho@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

dotnet/src/Microsoft.Agents.AI.Workflows.Generators/Models/MethodAnalysisResult.cs

@@ -0,0 +1,51 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI.Workflows.Generators.Models;
+
+/// <summary>
+/// Represents the result of analyzing a single method with [MessageHandler].
+/// Contains both the method's handler info and class context for grouping.
+/// Uses value-equatable types to support incremental generator caching.
+/// </summary>
+/// <remarks>
+/// Class-level validation (IsPartialClass, DerivesFromExecutor, HasManualConfigureRoutes)
+/// is extracted here but validated once per class in CombineMethodResults to avoid
+/// redundant validation work when a class has multiple handlers.
+/// </remarks>
+internal sealed record MethodAnalysisResult(
+    // Class identification for grouping
+    string ClassKey,
+
+    // Class-level info (extracted once per method, will be same for all methods in class)
+    string? Namespace,
+    string ClassName,
+    string? GenericParameters,
+    bool IsNested,
+    string ContainingTypeChain,
+    bool BaseHasConfigureRoutes,
+    ImmutableEquatableArray<string> ClassSendTypes,
+    ImmutableEquatableArray<string> ClassYieldTypes,
+
+    // Class-level facts (used for validation in CombineMethodResults)
+    bool IsPartialClass,
+    bool DerivesFromExecutor,
+    bool HasManualConfigureRoutes,
+
+    // Class location for diagnostics (value-equatable)
+    DiagnosticLocationInfo? ClassLocation,
+
+    // Method-level info (null if method validation failed)
+    HandlerInfo? Handler,
+
+    // Method-level diagnostics only (class-level diagnostics created in CombineMethodResults)
+    ImmutableEquatableArray<DiagnosticInfo> Diagnostics)
+{
+    /// <summary>
+    /// Gets an empty result for invalid targets (e.g., attribute on non-method).
+    /// </summary>
+    public static MethodAnalysisResult Empty { get; } = new(
+        string.Empty, null, string.Empty, null, false, string.Empty,
+        false, ImmutableEquatableArray<string>.Empty, ImmutableEquatableArray<string>.Empty,
+        false, false, false,
+        null, null, ImmutableEquatableArray<DiagnosticInfo>.Empty);
+}