fix: use event.handled guard before sending response

[pi0]

🔗 Linked issue

❓ 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

Use the new h3 event.handled flag (unjs/h3#410) to guard node.res.end calls and avoid responding to an already ended request similar to unjs/h3#411

📝 Checklist

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

[pi0]

/cc @danielroe We probably need to do the same for nuxt error handler for consistency.

[codecov]

Codecov Report

Merging #1326 (3e383f5) into main (46e6f10) will decrease coverage by 0.05%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##             main    #1326      +/-   ##
==========================================
- Coverage   76.59%   76.54%   -0.05%     
==========================================
  Files          70       70              
  Lines        7117     7121       +4     
  Branches      706      706              
==========================================
  Hits         5451     5451              
- Misses       1665     1669       +4     
  Partials        1        1              

Impacted Files	Coverage Δ
src/dev/error.ts	10.20% <16.66%> (-0.91%)	⬇️