Added playing song view. Adding styling to playing song. Fixed caching cancellation issue.

Harmonia.WinUI/Views/PlayingSongView.xaml.cs

@@ -0,0 +1,15 @@
+using Harmonia.WinUI.ViewModels;
+using Microsoft.UI.Xaml.Controls;
+
+namespace Harmonia.WinUI.Views;
+
+public sealed partial class PlayingSongView : UserControl
+{
+    private readonly PlayingSongViewModel _viewModel;
+
+    public PlayingSongView()
+    {
+        InitializeComponent();
+        _viewModel = (PlayingSongViewModel)DataContext;
+    }
+}