Contacts Refactor

[bbengfort]

Scope of changes

Refactors the contact handling library to simplify code and help resolve some of the contacts-related bugs we're seeing in the admin and other code.

Type of change

• bug fix
• new feature
• documentation
• other (refactor)

Acceptance criteria

Describe how reviewers can test this change to be sure that it works correctly. Add a checklist if possible

Author checklist

• I have manually tested the change and/or added automation in the form of unit tests or integration tests
• I have updated the dependencies list
• I have recompiled and included new protocol buffers to reflect changes I made
• I have added new test fixtures as needed to support added tests
• Check this box if a reviewer can merge this pull request after approval (leave it unchecked if you want to do it yourself)
• I have moved the associated Shortcut story to "Ready for Review"

Reviewer(s) checklist

• Any new user-facing content that has been added for this PR has been QA'ed to ensure correct grammar, spelling, and understandability.