Mark more things private

[shape-warrior-t]

Some modules, classes, and functions are not currently marked private, even when they are best thought of as implementation details of a specific subteam, module, or class. In particular, there are currently no modules in the codebase that are marked private. It might be a good idea to examine exactly what truly needs to be exposed to other subteams/modules/classes, and change public/private statuses of things accordingly.