chore: replace deprecated npm-run-all package

[lumirlumir]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

This PR is a follow-up to eslint/js#664 and eslint/generator-eslint#224.

In this PR, I've replaced npm-run-all with a native script.

Since npm-run-all is only used in a few places and, according to #137, is deprecated, removing this dev dependency would reduce maintenance overhead. Also, the existing script can be simplified by removing the npm-run-all package.

I've referenced the following script, which follows our package.json conventions.

• https://github.com/eslint/markdown/blob/main/package.json#L62-L63
• https://github.com/eslint/eslint-github-bot/blob/main/package.json#L7-L8
• https://github.com/eslint/rewrite/blob/main/package.json#L12-L13

What changes did you make? (Give an overview)

In this PR, I've replaced npm-run-all with a native script.

Related Issues

Ref: #137, eslint/js#664, eslint/generator-eslint#224

Is there anything you'd like reviewers to focus on?

N/A

[netlify]

✅ Deploy Preview for eslint-code-explorer ready!

Name	Link
🔨 Latest commit	fc0de75
🔍 Latest deploy log	https://app.netlify.com/projects/eslint-code-explorer/deploys/68cabe62701de0000891c7e0
😎 Deploy Preview	https://deploy-preview-153--eslint-code-explorer.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

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