🚀 Feature: Switch from tseslint.config to ESLint's defineConfig

[JoshuaKGoldberg]

Feature Request Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Coming over from JoshuaKGoldberg/eslint-fix-utils#244 -> JoshuaKGoldberg/eslint-fix-utils#245: as of typescript-eslint@8.42.0, tseslint.config is deprecated. The core ESLint defineConfig should be used instead. Let's make that change here!

Additional Info

https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.42.0

Co-authored-by: @michaelfaith

🎁