feat(math): support local katex assets and improve docs (#742)

* refactor(math): update LaTeX guide and enhance KaTeX integration

- Revised the LaTeX documentation for clarity and improved structure, changing section titles and descriptions for better understanding.
- Added support for chemistry expressions using the mhchem extension.
- Introduced a new KaTeX CSS loader partial to streamline the integration of KaTeX, allowing for configurable remote or local asset loading.
- Updated the head partial to utilize the new KaTeX loader, enhancing the flexibility of math rendering options.

* refactor(mathjax): simplify MathJax script URL configuration

- Removed the dynamic version assignment for MathJax and set a fixed version in the script URL for consistency and clarity.

* docs(latex): enhance LaTeX guide and clarify chemistry expressions

- Updated section titles for better clarity, changing "Supported Functions" to "Chemistry Expressions."
- Improved description of the mhchem extension for rendering chemistry equations.
- Removed redundant instructions regarding the passthrough extension in Hugo.
- Corrected minor typographical errors in references to MathJax.

layouts/_partials/scripts/mathjax.html

@@ -1,6 +1,5 @@
 {{/* MathJax */}}
-{{ $mathjaxVersion := site.Params.math.mathjaxVersion | default "3" -}}
-{{ $mathjaxJsUrl := printf "https://cdn.jsdelivr.net/npm/mathjax@%s/es5/tex-chtml.js" $mathjaxVersion -}}
+{{ $mathjaxJsUrl := "https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js" -}}
 <script defer id="MathJax-script" src="{{ $mathjaxJsUrl }}" crossorigin="anonymous" async></script>
 <script>
   MathJax = {