Improve diff lines count efficiency

Adds `# frozen_string_literal: true` to spec/models ruby files

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true

Signed-off-by: Rémy Coutable <remy@rymai.me>

The amount of precision times have in databases is variable, so we need
tolerances when comparing in specs. It's better to have the tolerance defined
in one place than several.

All the code that pre-calculates metrics for use in the cycle analytics
page.

- Ci::Pipeline -> build start/finish
- Ci::Pipeline#merge_requests
- Issue -> record default metrics after save
- MergeRequest -> record default metrics after save
- Deployment -> Update "first_deployed_to_production_at" for MR metrics
- Git Push -> Update "first commit mention" for issue metrics
- Merge request create/update/refresh -> Update "merge requests closing issues"