In 4.x, how to set the hierarchy of edges and nodes without setting groupByTypes, so that some edges are higher than nodes

### Describe the bug / 问题描述

在4.x下如何在不设置groupByTypes的情况下， 去设置edge和node的层级，让某些edge的层级高于node，还有是否可以单独设置某个node的层级，而不是单纯的置顶或置顶

### Reproduction link / 重现链接

_No response_

### Steps to Reproduce the Bug or Issue / 重现步骤

_No response_

### G6 Version / G6 版本

4.x

### Operating System / 操作系统

macOS, Windows

### Browser / 浏览器

Chrome

### Additional context / 补充说明

_No response_

The issue targets edge and node layering in G6 4.x, including behavior without groupByTypes and per-node ordering. No source files, tests, reproduction, or entry points are named; begin by locating the G6 4.x rendering and groupByTypes implementation, then determine the expected ordering behavior and add coverage for the requested cases.

Written by the indexing model from the issue text.