🏗️ Lint/format with the new ESLint/Biome configs

[blefnk]

Relivator 1.2.6 will introduce an updated ESLint config (it's officially flat, baybee)! The new ESLint v9 will become friends with Biome, and together they will say goodbye to Prettier (whom we will always remember, of course, but it's time to move on). Hey, no crying there—you will be able to add Prettier with the reliverse command after the release of Relivator 1.3.0.

I've been doing a lot of work to make things work nicely and smoothly with as many different kinds of codebases as Relivator users will throw at it. For almost everything, rules that don't support auto-fix are turned off by default; you can turn them back on at any time. Pssst... In that case, don't get caught with new bugs, hehe. Many important disabled things will be enabled starting from the next 1.3.0 version. Have fun with it!