refactor: remove dead_code and use spawn_blocking for fast_set

[hardfist]

Summary

use spawn_blocking for fast_drop & remove dead code

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for rspack ready!

Name	Link
🔨 Latest commit	91dc3bb
🔍 Latest deploy log	https://app.netlify.com/sites/rspack/deploys/6809dbda8fa9400008f4be3d
😎 Deploy Preview	https://deploy-preview-10151--rspack.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codspeed-hq]

CodSpeed Performance Report

Merging #10151 will not alter performance

_{Comparing yj/remove-deadcode (91dc3bb) with main (dbdfeb1)}

🎉 Hooray! codspeed-node just leveled up to 4.0.1!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

Summary

✅ 11 untouched benchmarks

[quininer]

LGTM