utilize modern c# features

ntfysh_client/NotificationDialog.cs

@@ -119,10 +119,7 @@ namespace ntfysh_client
 
         private void UpdateProgress(object? sender, EventArgs e)
         {
-            if (_shownStopwatch == null)
+            if (_shownStopwatch is null) return;
-            {
-                return;
-            }
 
             progress = (int)((_timeout - _shownStopwatch.ElapsedMilliseconds) * 100 / _timeout);
             lbTimeout.Text = $"{(int)(_timeout - _shownStopwatch.ElapsedMilliseconds) / 1000}";
@@ -146,11 +143,6 @@ namespace ntfysh_client
             base.SetVisibleCore(value);
         }
 
-        protected override void OnShown(EventArgs e)
-        {
-            base.OnShown(e);
-        }
-
         private void SetWindowPosition()
         {
             int workingtop = Screen.PrimaryScreen.WorkingArea.Height - Height;
@@ -188,21 +180,13 @@ namespace ntfysh_client
             }
         }
 
-        private Image? ConvertToolTipIconToImage(ToolTipIcon icon)
+        private Image? ConvertToolTipIconToImage(ToolTipIcon icon) => icon switch
         {
-            switch (icon)
+            ToolTipIcon.Info => SystemIcons.Information.ToBitmap(),
-            {
+            ToolTipIcon.Warning => SystemIcons.Warning.ToBitmap(),
-                case ToolTipIcon.Info:
+            ToolTipIcon.Error => SystemIcons.Error.ToBitmap(),
-                    return SystemIcons.Information.ToBitmap();
+            _ => null
-                case ToolTipIcon.Warning:
+        };
-                    return SystemIcons.Warning.ToBitmap();
-                case ToolTipIcon.Error:
-                    return SystemIcons.Error.ToBitmap();
-                case ToolTipIcon.None:
-                default:
-                    return null;
-            }
-        }
 
         private void InitializeWindowHidden()
         {
@@ -231,10 +215,7 @@ namespace ntfysh_client
             public const int AW_BLEND = 0x00080000;
         }
 
-        private void window_MouseDown(object sender, EventArgs e)
+        private void window_MouseDown(object sender, EventArgs e) => CancelTimer();
-        {
-            CancelTimer();
-        }
         
         private void CancelTimer()
         {