First added in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/139028, move `scripts/lint/unused_helper_methods.rb` to a state where it can be run automatically on `git push` (via LeftHook). Work remaining to be done: + https://gitlab.com/gitlab-org/gitlab/-/issues/436399+ (weighted separately from this issue) + Address "false positives` of routing helpers and class methods + add to automatic linters run via LeftHook