Added the Model Comparison assistant for blind comparisons of two models (#1009)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/Tests/Chat/Embedded/InMemoryEmbeddedChatStore.cs

@@ -0,0 +1,46 @@
+using AIStudio.Chat;
+using AIStudio.Chat.Embedded;
+
+namespace AIStudio.Tests.Chat.Embedded;
+
+/// <summary>
+/// Keeps embedded chats in memory, as they were when they were stored last.
+/// </summary>
+public sealed class InMemoryEmbeddedChatStore : IEmbeddedChatStore
+{
+    private readonly Dictionary<Guid, ChatThread> threads = [];
+
+    /// <summary>
+    /// Whether loading fails, as with a chat this version cannot open.
+    /// </summary>
+    public bool CannotOpen { get; init; }
+
+    /// <summary>
+    /// How often a chat was stored.
+    /// </summary>
+    public int SaveCount { get; private set; }
+
+    /// <summary>
+    /// Gets the blocks of a chat as they were stored last, or none.
+    /// </summary>
+    /// <param name="chatId">The ID of the chat.</param>
+    public IReadOnlyList<ContentBlock> StoredBlocks(Guid chatId) => this.threads.TryGetValue(chatId, out var thread) ? thread.Blocks : [];
+
+    /// <inheritdoc />
+    public Task<ChatThread?> LoadThreadAsync(Guid chatId, CancellationToken token = default)
+    {
+        if (this.CannotOpen)
+            throw new InvalidDataException("A newer version stored this chat.");
+
+        return Task.FromResult(this.threads.TryGetValue(chatId, out var thread) ? thread : null);
+    }
+
+    /// <inheritdoc />
+    public Task SaveThreadAsync(ChatThread thread, CancellationToken token = default)
+    {
+        // A copy of the list, so that what the chat adds later does not change what was stored:
+        this.threads[thread.ChatId] = thread with { Blocks = [.. thread.Blocks] };
+        this.SaveCount++;
+        return Task.CompletedTask;
+    }
+}