fix: configure dom-testing-library to flush Svelte changes

[mcous]

Overview

While working on new examples for Svelte 5, I found a problem with this library's interop with @testing-library/user-event - depending on project setup, await user.click() et. al. does not wait for Svelte to flush changes.

We were missing a call to configure to @testing-library/dom to configure the eventWrapper (for fireEvent) and asyncWrapper (for user-event) options. This fixes the issue for user-event, and happily, removes the need for an async re-export of fireEvent once we're able to drop Svelte 3/4, thanks to the new flushSync export from svelte

Related (old) issue: #250

Change log

• Add setup function to complement cleanup function that calls @testing-library/dom::configure with tick and flushSync
• Wire setup into beforeEach for Jest and Vitest
• Add cleanup setup to setup docs in README

[github-actions]

🎉 This PR is included in version 5.2.8 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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