feat: export ServerRequest from nitro/types

[NBruhno]

🔗 Linked issue

#3784

❓ 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

It might be a hard fetch to call it a "new feature", but this change makes it so the ServerRequest type from srvx is re-exported from nitro/types. This makes it easier to type functions, e.g. helper functions utilizing the useRequest() async context util.

This is the first time I'm contribution to anothers repo like this so let me know if I missed some steps or if there is something else needed.

I also have no issue if this change is unwanted, it is not a big deal to have to import the type from srvx instead.

Resolves #3784

📝 Checklist

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

[vercel]

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