feat(rehype-shikiji): support metastring from node.properties

[zce]

Description

Try to obtain the metastring from node.properties.metastring when node.data.meta does not exist

Linked Issues

#113

[netlify]

✅ Deploy Preview for shikiji ready!

Name	Link
🔨 Latest commit	13b742b
🔍 Latest deploy log	https://app.netlify.com/sites/shikiji/deploys/65b2b0de871c8b0008d9520f
😎 Deploy Preview	https://deploy-preview-114--shikiji.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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (57d298e) 97.27% compared to head (13b742b) 97.28%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #114   +/-   ##
=======================================
  Coverage   97.27%   97.28%           
=======================================
  Files          54       54           
  Lines        4956     4965    +9     
  Branches      639      639           
=======================================
+ Hits         4821     4830    +9     
  Misses        132      132           
  Partials        3        3           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.