Combine milk, carrots, rice, cardamom, cinnamon and ginger in a 4-qt. slow cooker. Stir in half the chopped pistachios. Cook, covered, on high heat for 2-1/2 hours, stirring occasionally. Add agave and raisins; reduce heat to low. Cover and cook until rice is tender, 15 minutes longer. If desired, stir in rose water. Serve warm or refrigerate and serve chilled. Garnish each serving with remaining pistachios.