Use Playwright for integration tests

We currently use Selenium to test the examples in our documentation for errors. This is useful, but it doesn't catch features silently failing. This happened in our v0.19.0 release.

We need tests that actually verify the expected elements are visible on the page. This requires work: for each example we have to define what elements are expected, possibly after clicking on some other element.

I'd like to try to use Playwright for this. It looks pretty easy to use. It also integrates with Pytest. I'll give this a shot on a couple examples to see if this approach works well. If so, we can apply it to all examples.

首先检查现有的、基于 Selenium 的文档示例集成测试，以及它们如何使用 Pytest 运行。在几个示例上尝试 Playwright，定义预期可见的元素和任何必需的点击操作。当该方法能够检测出静默失败的功能，并且可以一致地应用于所有示例时，即视为完成。