Unusual drawing occurs when there are a lot of polyline type lines

### Describe the bug / 问题描述

polyline类型的连线，如果存在很多会导致绘制异常

[我的场景：我多个节点是水平排列的（y值相同），每个节点之间的连线都是多对多，我将链接桩自定义在节点上方（例如[[0.25,0,[0.5,0]]），连接线使用polyline模式，通过设置offset来保证每条线有一定的间隔
目前问题：在连接线较少的情况下没问题，但是连接线多的情况下就导致绘制乱套了，求指教。



### Reproduction link / 重现链接

https://stackblitz.com/edit/react-sb7gk6?file=index.js

### 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

Windows

### Browser / 浏览器

Chrome

### Additional context / 补充说明

_No response_

Start with the linked StackBlitz reproduction in index.js and compare a few polyline connections with many connections using the described horizontal nodes, custom top ports, and offsets. Trace the rendering path exercised by that reproduction; done means dense links remain separated and render consistently.

Written by the indexing model from the issue text.