add class CenterDecorator and add method draw decoration

src/main/java/shape/CenterDecorator.java

+package shape;
+
+import javafx.scene.canvas.GraphicsContext;
+import javafx.scene.paint.Color;
+import javafx.geometry.Point2D;
+import shape.Shape;
+
+public class CenterDecorator extends Decorator{
+    private double radius;
+
+    public CenterDecorator(Shape decoratedShape, double radius){
+        super(decoratedShape);
+        this.radius=radius;
+    }
+
+    @Override
+    protected void drawDecoration(GraphicsContext graphicsContext) {
+        graphicsContext.setStroke(Color.RED);  // Définir la couleur de la décoration
+
+        // Calculer le centre de la forme décorée
+        Point2D center = point(0);
+
+        // Dessiner un cercle autour du centre
+        graphicsContext.fillOval(center.getX() - radius, center.getY() - radius, radius * 2, radius * 2);
+    }
+    public void draw(GraphicsContext graphicsContext) {
+        super.draw(graphicsContext);
+        drawDecoration(graphicsContext);
+    }
+}