feat: Notification API + 自定义渲染函数 + stack独立配置完善

src/core.js

@@ -246,6 +246,13 @@ class Toast {
   }
 
   _buildContent(el, c) {
+    // 自定义渲染函数 — 完全接管 DOM 构建
+    if (typeof this.config.render === 'function') {
+      el.innerHTML = this.config.render(this);
+      this.barEl = el.querySelector('.met-bar, .met-bar-v');
+      return;
+    }
+    
     const showIcon = this.config.icon !== false && (this.iconHTML || ICONS[this.type]);
     const showClose = this.config.closeButton !== false;
     const showProgress = this.config.showProgress !== false && this.config.duration > 0;