CLI to create `filename.twoslash.json` along with `filename.md` for pre-rendered content

[antfu]

We could have a standalone cli (also related to #14) that pass run Twoslash ahead of time to generate xxx.twoslash.json along with each markdown file, to serve as caches for other integrations to consume directly without the computational cost and complex setup, idea brought up by @danielroe at nuxt/nuxt#31353 (comment)