Forbid wildcard ("barrel") exports

When developing and maintaining a package, it is critical to understand what modules are being exported.

There are a couple ways to do this:

1. Add a test for the entrypoint of the package (`index.ts`), [like for `utils`](https://github.com/MetaMask/utils/blob/fb9440203099538670a4af95da16265f878f2cc9/src/index.test.ts).
2. Be explicit about which modules are being exported in the entrypoint.

I am proposing that we follow the second route as it is simpler. This would mean banning wildcard exports.

No ESLint rule exists per se to forbid wildcard exports, but evidently you can use `no-restricted-syntax` as a workaround as described here: https://github.com/import-js/eslint-plugin-import/issues/2493#issuecomment-1465462298

Start by inspecting the package's ESLint configuration and the `index.ts` entrypoint, then compare the `no-restricted-syntax` workaround with the linked ESLint discussion. Done means the configuration rejects wildcard exports while allowing explicit exports, with the behavior verified by the relevant lint check.

Written by the indexing model from the issue text.