.NET: Chathistory memory provider add (#1867)

* Add ChatHistoryMemoryProvider with unit tests

* Set new project to not packable.

* Fix bugs

* Add serialization support.

* Update dotnet/src/Microsoft.Agents.AI.VectorDataMemory/ChatHistoryMemoryProvider.cs

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

* Remove unnecessary line

* Convert ChatHistoryMemoryProvider to use Dynamic collections.

* Sealing options and scope classes.

* Add sample, add scope to logs and improve scope validation

* Move ChatHistoryMemoryProvider to MAAI project.

---------

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

dotnet/src/Microsoft.Agents.AI/Memory/ChatHistoryMemoryProviderOptions.cs

@@ -0,0 +1,56 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+namespace Microsoft.Agents.AI;
+
+/// <summary>
+/// Options controlling the behavior of <see cref="ChatHistoryMemoryProvider"/>.
+/// </summary>
+public sealed class ChatHistoryMemoryProviderOptions
+{
+    /// <summary>
+    /// Gets or sets a value indicating when the search should be executed.
+    /// </summary>
+    /// <value><see cref="SearchBehavior.BeforeAIInvoke"/> by default.</value>
+    public SearchBehavior SearchTime { get; set; } = SearchBehavior.BeforeAIInvoke;
+
+    /// <summary>
+    /// Gets or sets the name of the exposed search tool when operating in on-demand mode.
+    /// </summary>
+    /// <value>Defaults to "Search".</value>
+    public string? FunctionToolName { get; set; }
+
+    /// <summary>
+    /// Gets or sets the description of the exposed search tool when operating in on-demand mode.
+    /// </summary>
+    /// <value>Defaults to "Allows searching through previous chat history to help answer the user question.".</value>
+    public string? FunctionToolDescription { get; set; }
+
+    /// <summary>
+    /// Gets or sets the context prompt prefixed to results.
+    /// </summary>
+    public string? ContextPrompt { get; set; }
+
+    /// <summary>
+    /// Gets or sets the maximum number of results to retrieve from the chat history.
+    /// </summary>
+    /// <value>
+    /// Defaults to 3 if not set.
+    /// </value>
+    public int? MaxResults { get; set; }
+
+    /// <summary>
+    /// Behavior choices for the provider.
+    /// </summary>
+    public enum SearchBehavior
+    {
+        /// <summary>
+        /// Execute search prior to each invocation and inject results as a message.
+        /// </summary>
+        BeforeAIInvoke,
+
+        /// <summary>
+        /// Expose a function tool to perform search on-demand via function/tool calling.
+        /// </summary>
+        OnDemandFunctionCalling
+    }
+}