Do not create duo core todo if a user has already received one

What does this MR do and why?

Do not create duo core todo if a user has already received one

• regardless if it has bee 'cleared'/'done' or not
• resolve rubocop exceptions on files touched.
• improve finder specs.
• see https://gitlab.com/gitlab-org/gitlab/-/issues/548141

DB analysis: !193773 (comment 2551534158)

Changelog: other EE: true

How to set up and validate locally

1. Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK

2. Create a top level group.

3. In rails console change the duo_nano_features_enabled setting.

   Group.last.namespace_settings.update!(duo_nano_features_enabled: nil)
   Group.last.namespace_settings.update!(duo_nano_features_enabled: true)

4. Visit http://gdk.test:3000/admin/sidekiq/scheduled and force the sidekiq job seen below to run by adding it to the queue.

   Click to expand

   

5. Go to any user, part of that group, todos and notice the todo added.

6. Clear the todo(make it done) in the UI.

7. Repeat this whole process and ensure you don't see any new todos. Same group can be re-used if desired.

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