fix: fix restoring current pen to shape pen

When the user restarts the app and their last used tool was the ShapePen, the last tool is successfully restored but `Pen.currentPen` isn't updated.

lib/components/home/preview_card.dart

@@ -16,7 +16,6 @@ import 'package:saber/data/extensions/color_extensions.dart';
 import 'package:saber/data/file_manager/file_manager.dart';
 import 'package:saber/data/prefs.dart';
 import 'package:saber/data/routes.dart';
-import 'package:saber/i18n/strings.g.dart';
 import 'package:saber/pages/editor/editor.dart';
 
 class PreviewCard extends StatefulWidget {

lib/components/toolbar/pen_modal.dart

@@ -94,7 +94,7 @@ class _PenModalState extends State<PenModal> {
           ),
           IconButton(
             onPressed: () => setState(() {
-              widget.setTool(ShapePen.currentShapePen);
+              widget.setTool(ShapePen());
             }),
             style: TextButton.styleFrom(
               foregroundColor: Pen.currentPen.icon == ShapePen.shapePenIcon

lib/data/tools/shape_pen.dart

@@ -24,8 +24,6 @@ class ShapePen extends Pen {
     strokeProperties = Prefs.lastShapePenProperties.value;
   }
 
-  static Pen currentShapePen = ShapePen();
-
   static final log = Logger('ShapePen');
 
   static const IconData shapePenIcon = FontAwesomeIcons.shapes;

lib/pages/editor/editor.dart

@@ -138,10 +138,13 @@ class EditorState extends State<Editor> {
           Pen.currentPen = Pen.ballpointPen();
         }
         return Pen.currentPen;
+      case ToolId.shapePen:
+        if (Pen.currentPen.toolId != Prefs.lastTool.value) {
+          Pen.currentPen = ShapePen();
+        }
+        return Pen.currentPen;
       case ToolId.highlighter:
         return Highlighter.currentHighlighter;
-      case ToolId.shapePen:
-        return ShapePen.currentShapePen;
       case ToolId.eraser:
         return Eraser();
       case ToolId.select: