CmdPal: Update WebSearch extension history immediately (#41398)

## Summary of the Pull Request

This PR ensures that the list of recent searches in the Web Search
extension is updated immediately after a new item is added or when
settings controlling the number of items are changed.

- Refactors the Web Search extension history to keep it in memory after
being loaded at startup
- Adds an event to notify subscribers when the history changes  
- Implements `IDisposable` to ensure that `WebSearchListPage`
unsubscribes from the event
- Moves responsibility for creating all list items to single class
(`WebSearchListPage`)
- Updated unit tests
- 
## PR Checklist

- [x] Closes: #40548
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [x] **Tests:** Added/updated and all pass
- [x] **Localization:** All end-user-facing strings can be localized
- [x] **Dev docs:** nothing
- [x] **New binaries:** none
- [x] **Documentation updated:** nope

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.WebSearch.UnitTests/MockSettingsInterface.cs

@@ -2,10 +2,9 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Collections.Generic;
-using Microsoft.CmdPal.Ext.WebSearch.Commands;
 using Microsoft.CmdPal.Ext.WebSearch.Helpers;
-using Microsoft.CommandPalette.Extensions.Toolkit;
 
 namespace Microsoft.CmdPal.Ext.WebSearch.UnitTests;
 
@@ -13,34 +12,22 @@ public class MockSettingsInterface : ISettingsInterface
 {
     private readonly List<HistoryItem> _historyItems;
 
+    public event EventHandler HistoryChanged;
+
     public bool GlobalIfURI { get; set; }
 
-    public uint HistoryItemCount { get; set; }
+    public int HistoryItemCount { get; set; }
 
-    public MockSettingsInterface(uint historyItemCount = 0, bool globalIfUri = true, List<HistoryItem> mockHistory = null)
+    public IReadOnlyList<HistoryItem> HistoryItems => _historyItems;
+
+    public MockSettingsInterface(int historyItemCount = 0, bool globalIfUri = true, List<HistoryItem> mockHistory = null)
     {
         _historyItems = mockHistory ?? new List<HistoryItem>();
         GlobalIfURI = globalIfUri;
         HistoryItemCount = historyItemCount;
     }
 
-    public List<ListItem> LoadHistory()
-    {
-        var listItems = new List<ListItem>();
-        foreach (var historyItem in _historyItems)
-        {
-            listItems.Add(new ListItem(new SearchWebCommand(historyItem.SearchString, this))
-            {
-                Title = historyItem.SearchString,
-                Subtitle = historyItem.Timestamp.ToString("g", System.Globalization.CultureInfo.InvariantCulture),
-            });
-        }
-
-        listItems.Reverse();
-        return listItems;
-    }
-
-    public void SaveHistory(HistoryItem historyItem)
+    public void AddHistoryItem(HistoryItem historyItem)
     {
         if (historyItem is null)
         {
@@ -54,15 +41,18 @@ public class MockSettingsInterface : ISettingsInterface
         {
             while (_historyItems.Count > HistoryItemCount)
             {
-                _historyItems.RemoveAt(0); // Remove the oldest item
+                _historyItems.RemoveAt(0);
             }
         }
+
+        HistoryChanged?.Invoke(this, EventArgs.Empty);
     }
 
     // Helper method for testing
     public void ClearHistory()
     {
         _historyItems.Clear();
+        HistoryChanged?.Invoke(this, EventArgs.Empty);
     }
 
     // Helper method for testing

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.WebSearch.UnitTests/QueryTests.cs

@@ -45,7 +45,7 @@ public class QueryTests : CommandPaletteUnitTestBase
     }
 
     [TestMethod]
-    public async Task LoadHistoryReturnsExpectedItems()
+    public async Task HistoryReturnsExpectedItems()
     {
         // Setup
         var mockHistoryItems = new List<HistoryItem>
@@ -77,7 +77,7 @@ public class QueryTests : CommandPaletteUnitTestBase
     }
 
     [TestMethod]
-    public async Task LoadHistoryMoreThanLimitation()
+    public async Task HistoryExceedingLimitReturnsMaxItems()
     {
         // Setup
         var mockHistoryItems = new List<HistoryItem>
@@ -109,7 +109,7 @@ public class QueryTests : CommandPaletteUnitTestBase
     }
 
     [TestMethod]
-    public async Task LoadHistoryWithDisableSetting()
+    public async Task HistoryWhenSetToNoneReturnEmptyList()
     {
         // Setup
         var mockHistoryItems = new List<HistoryItem>

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.WebSearch.UnitTests/SettingsManagerTests.cs

@@ -0,0 +1,48 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading.Tasks;
+
+using Microsoft.CmdPal.Ext.UnitTestBase;
+using Microsoft.CmdPal.Ext.WebSearch.Helpers;
+using Microsoft.CmdPal.Ext.WebSearch.Pages;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Microsoft.CmdPal.Ext.WebSearch.UnitTests;
+
+[TestClass]
+public class SettingsManagerTests : CommandPaletteUnitTestBase
+{
+    [TestMethod]
+    public async Task HistoryChangedEventIsRaisedWhenItemIsAdded()
+    {
+        // Setup
+        var settings = new MockSettingsInterface(historyItemCount: 5);
+        var page = new WebSearchListPage(settings);
+
+        var eventRaised = false;
+
+        try
+        {
+            settings.HistoryChanged += Handler;
+
+            // Act
+            settings.AddHistoryItem(new HistoryItem("test event", DateTime.UtcNow));
+            await Task.Delay(50);
+
+            // Assert
+            Assert.IsTrue(eventRaised, "Expected HistoryChanged to be raised when saving history.");
+        }
+        finally
+        {
+            settings.HistoryChanged -= Handler;
+            page.Dispose();
+        }
+
+        return;
+
+        void Handler(object s, EventArgs e) => eventRaised = true;
+    }
+}