feat: add custom formatURL support

[mickaelalvs]

❓ Context

Adds a formatURL callback option to startCodeServer / createCodeServer, allowing callers to customize the URL returned by the server before it is handed back to the consumer.

const handle = await startCodeServer({
  defaultFolder: '/my/project',
  formatURL: (url) => {
    // open a specific file on startup
    url.searchParams.set(
      'payload',
      JSON.stringify([['openFile', `vscode-remote://remote/my/project/src/index.ts`]])
    )
    return url
  },
})

The callback receives the base URL after auth params (tkn) have been applied. It can return a modified URL, a plain string, or undefined (keep the original URL unchanged).

This replaces the previous openFile option with a more generic primitive — callers can now inject any URL parameter VS Code supports (payload, folder, etc.) without requiring dedicated options in coderaft itself.

[mickaelalvs]

📝 note: CI fixed with #5 😊

[pi0]

Wondering if it might be more useful to instead add a generic formatURL(url: URL): string | URL | undefined callback option that accepts original url and allows customizing it. I guess we might have more options than openFile

[mickaelalvs]

Yes, that’s exactly what I thought after creating this PR, I’ve already seen other use cases 😅 I’ll have a look!

[mickaelalvs]

@pi0 I've tried to make the function more generic so that we can add more options 😊

[pi0]

thnx!