onPanelToggle property
面板显示/隐藏回调（可选）/ Panel toggle callback (optional) 点击按钮时触发，由外部决定如何显示面板 / Triggered when button is clicked, external decides how to show panel 如果为 null，则内部自动管理面板 / If null, manages panel internally
Implementation
final VoidCallback? onPanelToggle;