🚀 Feature: Replace bespoke types with mdast types

### Bug Report Checklist - [x] I have tried restarting my IDE and the issue persists. - [x] I have pulled the latest `main` branch of the repository. - [x] I have [searched for related issues](https://github.com/JoshuaKGoldberg/sentences-per-line/issues?q=is%3Aissue) and found none that matched my issue. ### Overview The `prettier-plugin-sentence-per-line` package has its own hand-crafted node types. The prettier markdown plugin uses `@types/mdast` under the covers. Recommend replacing the hand-crafted types with `mdast` ones. - https://github.com/syntax-tree/mdast - https://www.npmjs.com/package/@types/mdast ### Additional Info _No response_