使用groupByTypes和自定义节点/combo后层级混乱

### 问题描述

连接线与节点、combo完全混乱，我只想要连接线始终居于最底层，我在issue看了很多方法，都试了，不得行，怪得很

### 重现链接

https://github.com/Shen120/bugs-g6.git

### 重现步骤

拉代码，然后run

### 预期行为

连接线始终居于最底层

### 平台

- 操作系统: [macOS, Windows, Linux, React Native ...]
- 网页浏览器: [Google Chrome, Safari, Firefox]
- G6 版本: 4.8.24

### 屏幕截图或视频（可选）


### 补充说明（可选）
```这个例子也会出现层级混乱```

[_例子 ](https://codesandbox.io/p/devbox/g6-additem-9svhy9?file=%2Fsrc%2FApp.tsx%3A19%2C19&layout=%257B%2522sidebarPanel%2522%253A%2522EXPLORER%2522%252C%2522rootPanelGroup%2522%253A%257B%2522direction%2522%253A%2522horizontal%2522%252C%2522contentType%2522%253A%2522UNKNOWN%2522%252C%2522type%2522%253A%2522PANEL_GROUP%2522%252C%2522id%2522%253A%2522ROOT_LAYOUT%2522%252C%2522panels%2522%253A%255B%257B%2522type%2522%253A%2522PANEL_GROUP%2522%252C%2522contentType%2522%253A%2522UNKNOWN%2522%252C%2522direction%2522%253A%2522vertical%2522%252C%2522id%2522%253A%2522clv4ocsa40007356mdt9ld0ks%2522%252C%2522sizes%2522%253A%255B100%252C0%255D%252C%2522panels%2522%253A%255B%257B%2522type%2522%253A%2522PANEL_GROUP%2522%252C%2522contentType%2522%253A%2522EDITOR%2522%252C%2522direction%2522%253A%2522horizontal%2522%252C%2522id%2522%253A%2522EDITOR%2522%252C%2522panels%2522%253A%255B%257B%2522type%2522%253A%2522PANEL%2522%252C%2522contentType%2522%253A%2522EDITOR%2522%252C%2522id%2522%253A%2522clv4ocsa30002356m3oycaugx%2522%257D%255D%257D%252C%257B%2522type%2522%253A%2522PANEL_GROUP%2522%252C%2522contentType%2522%253A%2522SHELLS%2522%252C%2522direction%2522%253A%2522horizontal%2522%252C%2522id%2522%253A%2522SHELLS%2522%252C%2522panels%2522%253A%255B%257B%2522type%2522%253A%2522PANEL%2522%252C%2522contentType%2522%253A%2522SHELLS%2522%252C%2522id%2522%253A%2522clv4ocsa30004356mj4qtgqag%2522%257D%255D%252C%2522sizes%2522%253A%255B100%255D%257D%255D%257D%252C%257B%2522type%2522%253A%2522PANEL_GROUP%2522%252C%2522contentType%2522%253A%2522DEVTOOLS%2522%252C%2522direction%2522%253A%2522vertical%2522%252C%2522id%2522%253A%2522DEVTOOLS%2522%252C%2522panels%2522%253A%255B%257B%2522type%2522%253A%2522PANEL%2522%252C%2522contentType%2522%253A%2522DEVTOOLS%2522%252C%2522id%2522%253A%2522clv4ocsa40006356ml12m55z4%2522%257D%255D%252C%2522sizes%2522%253A%255B100%255D%257D%255D%252C%2522sizes%2522%253A%255B50%252C50%255D%257D%252C%2522tabbedPanels%2522%253A%257B%2522clv4ocsa30002356m3oycaugx%2522%253A%257B%2522tabs%2522%253A%255B%257B%2522id%2522%253A%2522clv4ocsa30001356m1ea5www2%2522%252C%2522mode%2522%253A%2522permanent%2522%252C%2522type%2522%253A%2522FILE%2522%252C%2522filepath%2522%253A%2522%252FREADME.md%2522%252C%2522state%2522%253A%2522IDLE%2522%257D%252C%257B%2522id%2522%253A%2522clv5znc7a0002356mnz4l7b9z%2522%252C%2522mode%2522%253A%2522permanent%2522%252C%2522type%2522%253A%2522FILE%2522%252C%2522initialSelections%2522%253A%255B%257B%2522startLineNumber%2522%253A19%252C%2522startColumn%2522%253A19%252C%2522endLineNumber%2522%253A19%252C%2522endColumn%2522%253A19%257D%255D%252C%2522filepath%2522%253A%2522%252Fsrc%252FApp.tsx%2522%252C%2522state%2522%253A%2522IDLE%2522%257D%255D%252C%2522id%2522%253A%2522clv4ocsa30002356m3oycaugx%2522%252C%2522activeTabId%2522%253A%2522clv5znc7a0002356mnz4l7b9z%2522%257D%252C%2522clv4ocsa40006356ml12m55z4%2522%253A%257B%2522tabs%2522%253A%255B%257B%2522id%2522%253A%2522clv4ocsa40005356mappr1vl5%2522%252C%2522mode%2522%253A%2522permanent%2522%252C%2522type%2522%253A%2522TASK_PORT%2522%252C%2522taskId%2522%253A%2522dev%2522%252C%2522port%2522%253A5173%252C%2522path%2522%253A%2522%252F%2522%257D%255D%252C%2522id%2522%253A%2522clv4ocsa40006356ml12m55z4%2522%252C%2522activeTabId%2522%253A%2522clv4ocsa40005356mappr1vl5%2522%257D%252C%2522clv4ocsa30004356mj4qtgqag%2522%253A%257B%2522id%2522%253A%2522clv4ocsa30004356mj4qtgqag%2522%252C%2522tabs%2522%253A%255B%257B%2522id%2522%253A%2522clv4ocsa30003356mvckb5r0o%2522%252C%2522mode%2522%253A%2522permanent%2522%252C%2522type%2522%253A%2522TASK_LOG%2522%252C%2522taskId%2522%253A%2522dev%2522%257D%255D%252C%2522activeTabId%2522%253A%2522clv4ocsa30003356mvckb5r0o%2522%257D%257D%252C%2522showDevtools%2522%253Atrue%252C%2522showShells%2522%253Afalse%252C%2522showSidebar%2522%253Atrue%252C%2522sidebarPanelSize%2522%253A15%257D)

Clone and run the linked reproduction repository, then inspect the example entry point at src/App.tsx around line 19, focusing on the groupByTypes, custom node, and combo setup. Reproduce the layering problem and verify that connection lines remain below nodes and combos in the rendered graph.

Written by the indexing model from the issue text.