fix: upgrade unimport to support autoImport: false

[antfu]

🔗 Linked issue

close #1288

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 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)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

I implemented it in the unplugin of unimport. So there is nothing need to do on nitro side other than upgrade.

📝 Checklist

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

[pi0]

👍🏼

(for the context, previously, we had #imports alias to the nitro core imports when plugin was being disabled. this seems better as also brings user/h3 imports)

[pi0]

Upgrade to 3.0.8 is done in main branch (Thanks for PR BTW!)