feat: add Typst support as alternative formula renderer

[KHemanthRaju]

This PR adds support for Typst as an alternative to KaTeX for formula rendering in Slidev.

Features

• Added a new formulaRenderer option in frontmatter to choose between 'katex' (default) and 'typst'
• Implemented Typst.ts integration for rendering Typst formulas
• Added line highlighting support for Typst formulas
• Created documentation for Typst usage

Usage

To use Typst as the formula renderer, add this to your frontmatter:

---
formulaRenderer: typst
---

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[antfu]

There is already a community addons for that https://github.com/slidevjs/slidev/pull/2179, have you tried it? If it works well I don't think we need to have it builtin

[peekxc]

There is already a community addons for that https://github.com/slidevjs/slidev/pull/2179, have you tried it? If it works well I don't think we need to have it builtin

Well, to be clear these are different features. Consider this slide, which uses both typst and katex:

---
addons:
  - slidev-addon-typst
---

Given pair of graphs $(H, G)$, determine *if there exists* an injective map $f: V_H \to V_G$ satisfying: 

'''typst
$ (v,v') in E_H <==> (f(v), f(v')) in E_G $ 
'''

vs this slide, which would use typst exclusively via the proposed change:

---
formulaRenderer: typst
---

Given pair of graphs $(H, G)$, determine *if there exists* an injective map $f: V_H to V_G$ satisfying: 

$ (v,v') in E_H <==> (f(v), f(v')) in E_G $ 

Neither the typst plugin nor MDC apparently supports inline syntax, I don't see how to avoid using katex for inline changes, but this is unfavorable.