Update to Vitest 4.1

[HiDeoo]

Description

In #3644, Vitest was updated to version 4.1.0-beta.6. Now that 4.1.0 is released, this PR updates to the stable version.

The migration in #3644 was also made in the less disruptive way possible considering the amount of changes in the PR. This PR uses some of the new APIs, removes some now deprecated APIs, etc. from the version 4.0 and 4.1.

Each change are in dedicated commits, where the commit message contains a link to the relevant section of the Vitest changelog, if any.

[netlify]

✅ Deploy Preview for astro-starlight ready!

Name	Link
🔨 Latest commit	aa58beb
🔍 Latest deploy log	https://app.netlify.com/projects/astro-starlight/deploys/69b3f2c0010d0b0008aa99a4
😎 Deploy Preview	https://deploy-preview-3757--astro-starlight.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 100 (no change from production) Accessibility: 100 (no change from production) Best Practices: 100 (no change from production) SEO: 100 (no change from production) PWA: - View the detailed breakdown and full score reports

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[changeset-bot]

⚠️ No Changeset found

Latest commit: aa58beb

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[delucis]

Thank you @HiDeoo! I’d considered updating this, but definitely would have missed some of these details 🚀