Clean up aggregation and scaling tests

[chacalle]

Describe changes

• Separate aggregation & scaling tests from each other for readability. Will delete test_agg_scale.R later

• Also remove tests that were testing features/expectations already tested.

• Improve descriptions to better match with the function design and description (not specific to age/year/location etc.)

• Update to style guide

What issues are related

Related to #51

Checklist

Packages Repositories

• [X] Have you read the contributing guidelines for ihmeuw-demographics R packages?
• [x] Have you successfully run devtools::check() locally?
• [X] Have you updated or added function (and vignette if applicable) documentation? Did you update the 'man' and 'NAMESPACE' files with devtools::document()?
• [X] Have you added in tests for the changes included in the PR?
• [X] Do the changes follow the ihmeuw-demographics code style?
• [ ] Do the changes need to be immediately included in a new build of docker-base or docker-internal? If so follow directions in those repositories to rebuild and redeploy the images.
• [ ] Do the changes require updates to other repositories which use this package? If yes, make the necessary updates in those repos, and consider integration tests for those repositories.

Details of PR

We should check that all the features we want in the aggregation/scaling function have appropriate example data/tests #51 #53

[chacalle]

Have now finished cleaning/clarifying the existing tests. It would be helpful to review the tests we currently have (at least the descriptions of the different test scenarios) and brainstorm any other use cases we need to account for. #51 #53

Remaining tasks I will add in separate PRs:

• [X] add vignette profiling how fast these functions are on large datasets #55
• [X] add na_value_severity functionality and tests
• [X] ~see if square argument is still needed for additional speed ups~ #55