docs: update description for build close method

[chenjiahan]

Summary

Clarify the behavior of the close() method of rsbuild.build() and ensure consistent across different documentation files.

Checklist

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

[netlify]

✅ Deploy Preview for rsbuild ready!

Name	Link
🔨 Latest commit	155f823
🔍 Latest deploy log	https://app.netlify.com/sites/rsbuild/deploys/67d3a01610a37c000811abb6
😎 Deploy Preview	https://deploy-preview-4786--rsbuild.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
Lighthouse	1 paths audited Performance: 67 (🟢 up 2 from production) Accessibility: 97 (no change from production) Best Practices: 100 (no change from production) SEO: 100 (no change from production) PWA: 60 (no change from production) View the detailed breakdown and full score reports

---

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