chore: map npm package links to npmx.dev (#498)

Point npm package page links to npmx.dev instead of npmjs.org.

- **README.md**: Update `[npm-url]` and `[download-url]` badge links to
`https://npmx.dev/package/npminstall`

<!-- START COPILOT CODING AGENT TIPS -->
---

✨ Let Copilot coding agent [set things up for
you](https://github.com/cnpm/npminstall/issues/new?title=✨+Set+up+Copilot+instructions&body=Configure%20instructions%20for%20this%20repository%20as%20documented%20in%20%5BBest%20practices%20for%20Copilot%20coding%20agent%20in%20your%20repository%5D%28https://gh.io/copilot-coding-agent-tips%29%2E%0A%0A%3COnboard%20this%20repo%3E&assignees=copilot)
— coding agent works faster and does higher quality work when set up for
your repo.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: fengmk2 <156269+fengmk2@users.noreply.github.com>

Author: Copilot

README.md

@@ -8,13 +8,13 @@
 [![FOSSA Status](https://app.fossa.com/api/projects/git%2Bgithub.com%2Fcnpm%2Fnpminstall.svg?type=shield)](https://app.fossa.com/projects/git%2Bgithub.com%2Fcnpm%2Fnpminstall?ref=badge_shield)
 
 [npm-image]: https://img.shields.io/npm/v/npminstall.svg?style=flat-square
-[npm-url]: https://npmjs.org/package/npminstall
+[npm-url]: https://npmx.dev/package/npminstall
 [codecov-image]: https://codecov.io/gh/cnpm/npminstall/branch/master/graph/badge.svg
 [codecov-url]: https://codecov.io/gh/cnpm/npminstall
 [snyk-image]: https://snyk.io/test/npm/npminstall/badge.svg?style=flat-square
 [snyk-url]: https://snyk.io/test/npm/npminstall
 [download-image]: https://img.shields.io/npm/dm/npminstall.svg?style=flat-square
-[download-url]: https://npmjs.org/package/npminstall
+[download-url]: https://npmx.dev/package/npminstall
 
 Make `npm install` fast and handy.