refactor(eslint): top-level eslint

[TalDerei]

references #723

Removes eslint-config-custom package and implements top-level flat ESLint configuration, serving as the the primary linter configuration for all packages. package specific .eslintrc.cjs files are instructed to use the configuration defined in the top-level, and it more explicitly specifies the package's tsconfig.json for TypeScript-related linting.

[grod220]

Curious, do you think this solves a problem we have? The current config we have seems to be a turborepo standard thing. Moving it to the top level seems to be a net-neutral effect.

[TalDerei]

I think by removing dedicated configuration packages and leveraging inheritance, it has the nice property of reducing potential duplication. Since it extends the top-level configuration, it's also clearer when there are package-specific overrides, which can make it easier to read. This applies to the tsconfig.json as well.

I was sequentially going down the NPM publishing tracking issue to reduce our backlog.

[grod220]

I suppose my observation is that it doesn't remove the need for dedicated configs, it was using inheritance before, and there does not seem to be any de-duplication. At best, it seems like a net-neutral change. And in that case, I think it's best to stick with the default turborepo recommendation.