Removing Public Data Types from Service Layer (WIP)

[yimmyj]

Info

Closes #326.

Description

Refactoring every service-level file, replacing public types in the promises of methods with private types / models.

Changes

• Every Service / references to refactored methods

Type of Change

• Patch (non-breaking change/bugfix)
• Minor (non-breaking change which adds functionality)
• Major (fix or feature that would cause existing functionality to not work as
  expected)
• Documentation (A change to a README/description)
• Continuous Integration/DevOps Change (Related to deployment steps, continuous integration
  workflows, linting, etc.)
• Other: (Fill In)

If you've selected Patch, Minor, or Major as your change type, make sure to bump the version before merging in package.json!

Testing

I have tested that my changes fully resolve the linked issue ...

• locally.
• on the testing API/testing database.
• with appropriate Postman routes. Screenshots are included below.

Checklist

• I have performed a self-review of my own code.
• I have followed the style guidelines of this project.
• I have appropriately edited the API version in the package.json file.
• My changes produce no new warnings.

Screenshots

[github-actions]

Thanks for contributing!
If you've made changes to the API's functionality, please make sure to bump the package
version—see this guide to semantic versioning for details—and
document those changes as appropriate.