Migrate tests from AVA to Vitest

[chfoidl]

⚡ Improvements

• Migrate all package tests from AVA to Vitest via shared @drupal-kit/config-vitest runner that preserves existing test, test.serial, and t.* APIs without changing test logic
• Add per-package vitest.config.ts with sequential in-file execution for MSW-backed integration tests
• Convert snapshot tests to Vitest __snapshots__ format and remove legacy AVA snapshot directories

[changeset-bot]

🦋 Changeset detected

Latest commit: fe5b044

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@drupal-kit/core	Patch
@drupal-kit/consumers	Patch
@drupal-kit/jsonapi	Patch
@drupal-kit/simple-oauth-auth-code	Patch
@drupal-kit/simple-oauth	Patch
@drupal-kit/user-api	Patch
@drupal-kit/verification	Patch
@drupal-kit/types	Patch
@drupal-kit/eslint-config	Patch
@drupal-kit/config-prettier	Patch
@drupal-kit/config-typescript	Patch
@drupal-kit/config-vitest	Patch

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