Need to make the ..._write functions consistent across different types

For example, the `yaml_write` function returns a string while the `json_write` function actually writes content to the given file. Cursory thoughts:

- `..._write` functions should accept a file path and write to that file
- `..._to_string` functions should be the naming convention we use for a function that converts a given data structure to a string (e.g. `yaml_write`)

Start by locating the yaml_write, json_write, and other ..._write functions, then compare how each handles file paths and returned strings. Define the consistent naming and behavior from the issue's proposed conventions; the work is done when all affected functions follow one clear API.

Written by the indexing model from the issue text.