Migrate unit test runner from Jest to Vitest

[Copilot]

This PR migrates the repository’s test infrastructure from Jest to Vitest to standardize on a modern ESM-native runner while preserving existing test behavior. The change is limited to test tooling and test entrypoints.

• Tooling migration

  • Replaced jest with vitest in devDependencies.
  • Updated the test script to run Vitest directly.

• Configuration cleanup

  • Removed obsolete jest.config.js now that Jest is no longer used.

• Test compatibility updates

  • Updated the test file to import test globals explicitly from Vitest (test, expect), matching current ESM usage.

{
  "scripts": {
    "test": "vitest run"
  },
  "devDependencies": {
    "vitest": "^4.1.9"
  }
}

import { expect, test } from "vitest";

[JoyceZhu]

@copilot update the whole Babel toolchain to v8.0.0 and above; js-yaml to v5.0.0 and above; markdown-it to 14.2.0 and above.

[Copilot]

@copilot update the whole Babel toolchain to v8.0.0 and above; js-yaml to v5.0.0 and above; markdown-it to 14.2.0 and above.

Addressed in a8b0394.

• Updated @github/markdownlint-github to ^0.8.2, which upgrades its transitive markdown-it to 14.2.0.
• js-yaml is at ^5.1.0.
• There are no @babel/* packages in the current lockfile/dependency graph after the Jest removal, so no Babel versions below 8 remain in resolved dependencies.

[Copilot]

Pull request overview

Migrates the repository’s unit test runner from Jest to Vitest to better support ESM-native testing while keeping the existing test behavior.

Changes:

• Switched the test npm script from running Jest (with --experimental-vm-modules) to vitest run.
• Replaced Jest with Vitest in devDependencies and updated the test entrypoint to import Vitest globals explicitly.
• Removed the obsolete jest.config.js.

Show a summary per file

File	Description
src/index.test.js	Imports test/expect from Vitest to match the new test runner.
package.json	Updates the test script and devDependencies to use Vitest instead of Jest.
jest.config.js	Removes the Jest configuration file since Jest is no longer used.

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• Files reviewed: 2/4 changed files
• Comments generated: 1
• Review effort level: Low