Handle private package npm metadata fetching failures better

Clear and concise description of the problem

When fetching npm meta for private packages, it prints warnings like:

Failed to get npm meta for: [ 'undefined@undefined' ]

I know the private package's meta can't be fetched from the https://npm.antfu.dev/ endpoint, but it seems the error wasn't handled correctly.

Suggested solution

https://github.com/antfu/node-modules-inspector/blob/2573b65652b20fff01f39e685432f8861c002c89/packages/node-modules-inspector/src/shared/version-info.ts#L24-L31

The result might be:

{
  url: '/...',
  statusCode: 500,
  statusMessage: '',
  message: '[GET] "https://registry.npmjs.org/some-private-package": 404 Not Found'
}

We could either handle this to improve the warning logs (insteas of undefined@undefined)
or fetch npm meta using current private registry URL (e.g., https://private-registry.com/some-private-package)

Alternative

No response

Additional context

I'm willing to submit a PR for this. 🙌🏻

Validations

• Follow our Code of Conduct
• Read the Contributing Guide.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Start in packages/node-modules-inspector/src/shared/version-info.ts around lines 24–31 and reproduce the warning while fetching metadata for a private package. Determine whether the implementation should use the current private registry or improve the failed-fetch warning; done means the selected behavior no longer reports the package as undefined@undefined.