feat: config reload support for nitro dev

[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

Using new c12.watchConfig to watch nitro configuration and auto-reload.

Note: This only enables watch for nitro dev and not external frameworks like Nuxt. Nuxt CLI should adopt c12 watcher itself.

Note: This PR also unlocks HMR support for nitro 🚀

📝 Checklist

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

[codecov]

Codecov Report

Merging #1173 (14eef49) into main (3313207) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head 14eef49 differs from pull request most recent head 5b0f11a. Consider uploading reports for the commit 5b0f11a to get more accurate results

@@            Coverage Diff             @@
##             main    #1173      +/-   ##
==========================================
+ Coverage   76.78%   76.83%   +0.04%     
==========================================
  Files          67       67              
  Lines        6501     6514      +13     
  Branches      690      691       +1     
==========================================
+ Hits         4992     5005      +13     
  Misses       1508     1508              
  Partials        1        1              

Impacted Files	Coverage Δ
src/nitro.ts	89.42% <100.00%> (+0.31%)	⬆️
src/options.ts	96.18% <100.00%> (+0.08%)	⬆️
src/types/nitro.ts	100.00% <100.00%> (ø)

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