refactor(event): use sendWebResponse for event.respondWith

[pi0]

🔗 Linked issue

❓ 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

This PR deprecates legacy H3Request/H3Headers and uses new sendWebResponse utility for event.respondWith in order to reduce bundle size and uses latest/consistent response handling.

📝 Checklist

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

[codecov]

Codecov Report

Merging #481 (5fe5904) into main (bc202c0) will increase coverage by 0.94%.
The diff coverage is 79.16%.

@@            Coverage Diff             @@
##             main     #481      +/-   ##
==========================================
+ Coverage   81.30%   82.25%   +0.94%     
==========================================
  Files          28       28              
  Lines        3236     3206      -30     
  Branches      489      489              
==========================================
+ Hits         2631     2637       +6     
+ Misses        605      569      -36     

Files Changed	Coverage Δ
src/event/event.ts	90.36% <40.00%> (+15.59%)	⬆️
src/utils/response.ts	74.69% <66.66%> (+<0.01%)	⬆️
src/event/index.ts	100.00% <100.00%> (ø)
src/event/polyfills/headers.ts	42.64% <100.00%> (ø)
src/event/polyfills/response.ts	38.09% <100.00%> (ø)