Node Shape Passed to customizeTOC Not unified Standard

[shellscape]

The shape of the node object passed to customizeTOC doesn't match the Node interface as specified by the latest version of unified. This is what the plugin is passing:

{
    type: 'element',
    tagName: 'ol',
    properties: { className: 'toc toc-level toc-level-1' },
    children: [ [Object] ]
  }

This is what unified expects:

interface Node {
  type: string
  data: Data?
  position: Position?
}

As a result, we've no way to export the TOC using that method to stringify it, store the AST separately, etc.

[ChristianMurphy]

rehype and hast have official typings for the HTML nodes.
You can find them at https://www.npmjs.com/package/@types/hast

The overall plugin can leverage the Plugin type, for example import('unified').Plugin<[Options] | Array<void>, Root>} (for example: https://github.com/rehypejs/rehype-meta/blob/e5eae88704c300393641c71b9e3f59a780fc3ed7/lib/index.js#L145)

Everything in src/types.ts could probably be replaced with @types/hast.
And the guard in src/type-guards.ts could be simplified after @types/hast is in use, there are a few ways to narrow nodes https://unifiedjs.com/learn/recipe/narrow-node-typescript/