fix: improve autoImports deprecation dx

[pi0]

🔗 Linked issue

#6864

❓ 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

This PR tries to reduce breaking change surface and DX with refactor we made in #6864 to rename autoImports to imports and adds some left over refactors.

• Upgrading unjs/hookable to 5.3:
  • Deprecation warnings with same message are only shown once
  • New hook (name, fn, { allowDeprecated: true } to suppress the warning message
• Updated kit utils:
  • Soft deprecated (type only) addAutoImport to addImports and addAutoImportDir to addImportsDir for consistency
  • Use autoImport: hook (and suppressed warning) for backward compatibility until new hooks are widely adopted
• Moved deprecation to the core because it is impossible to use suppress with delayed deprecation
• Improved deprecation message to advice using @nuxt/kit utils with rc.9 instead of just new hook name.

Migration guide for module authors:

• Update @nuxt/kit dependency to ^3.0.0-rc.9 (this works for users with < rc.9)
• Use kit utils addImports and addImportsDir instead of directly using hooks

📝 Checklist

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

[netlify]

✅ Deploy Preview for nuxt3-docs canceled.

Name	Link
🔨 Latest commit	a7b2461
🔍 Latest deploy log	https://app.netlify.com/sites/nuxt3-docs/deploys/6311e53e847fe70007aea415

[antfu]

This is nice! Thanks!