chore: add src/types.ts to knip entry configuration

[Pixel998]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

This PR configures knip to properly recognize public API types in src/types.ts files so they aren't incorrectly flagged as unused exports. These types are meant for external consumption by package users, even if they're not used internally within our codebase.

What changes did you make? (Give an overview)

Added src/types.ts to the knip entry configuration for four packages that export public types:

• @eslint/config-array
• @eslint/config-helpers
• @eslint/migrate-config
• @eslint/plugin-kit

The @eslint/object-schema package already had this configuration.

Related Issues

#351

Is there anything you'd like reviewers to focus on?

[fasttime]

I believe knip is already recognizing src/types.ts files; otherwise it would flag them as unused. The issue in #351 seems to be an unreferenced type definition. I’ve added a comment on the PR with a possible fix.