Change Request: Add Knip to detect unused dependencies and exports

### Which packages would you like to change?

- [ ] `espree`
- [ ] `eslint-scope`
- [ ] `eslint-visitor-keys`

### What problem do you want to solve?

Unused dependencies, exports, and files can accumulate, adding unnecessary bloat and maintenance overhead. For example, in PR #690, many unused dependencies were removed manually, which could have been detected automatically.

### What do you think is the correct solution?

Add [Knip](https://knip.dev/) to the repo to automatically find unused dependencies, exports, and files. This would reduce manual cleanup, catch issues earlier, and keep the codebase lean, similar to its use in the eslint/eslint repo.

### Participation

- [x] I am willing to submit a pull request for this change.

### Additional comments

If the team agrees, I’d like to apply this to the other repos as well.