feat: upgrade to rollup v4

[pi0]

🔗 Linked issue

resolves #1794

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Upgrade to rollup v4

• Almost a month passed enough for ecosystem adoption (1)
• Vite v5 is out powered by roll-up v4 (https://vitejs.dev/blog/announcing-vite5)
• Additional ecosystem tests via Nuxt are pending for nightly

Important notes

• This makes the minimum Node.js version for (building) Nitro to v18

(1) Dependency issues: Only rollup-plugin-visualizer seems behind now:

 WARN  Issues with peer dependencies found
.
└─┬ rollup-plugin-visualizer 5.9.2
  └── ✕ unmet peer rollup@"2.x || 3.x": found 4.5.0

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.