perf: calculate permalink field only when needed

[SukkaW]

What does it do?

We don't necessarily need to calculate all potentially available fields of the permalink in advance. I myself never use hash or any dates in my permalink.

We should not have to deal with moment.js or sha1 overhead. We can actually calculate those expensive fields on demand.

I use foxts because I happen to have this exist in my util library. But I can always copy the implementation to hexo-util if needed.

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[github-actions]

How to test

git clone -b perf-on-demand-post-metadata https://github.com/SukkaW/hexo.git
cd hexo
npm install
npm test

[D-Sketon]

It looks like hexo-util's Permalink also needs modification, so may be a good time to incorporate the optimizations into hexo-util?