export wstest

Pipe function here: https://github.com/nhooyr/websocket/blob/master/internal/test/wstest/pipe.go#L17 is inside the internal package which means it can't be imported by other projects.
However it should be external so that it can be imported by other projects. This could help in unit testing of the projects

从 internal/test/wstest/pipe.go 第 17 行开始，检查 Pipe 函数的打包和引用方式。在保留其测试用途的同时，使外部 Go 项目可以导入该实用工具，然后验证下游项目无需依赖 internal 包即可访问它。

由索引模型根据 Issue 内容生成。