Reformat `downloader` subpackage

[brodycritchlow]

L18 is our main function, but it seems a little too bulky. We should split the download and installation into separate functions to prevent confusion within our codebase.

L19 and L149 have the same function; we should use some Enum value to condense them into one package (see below for the proposed solution). One problem with this solution is that now we have a constant return value of Vec<String> so we will have to account for that within our other functions

#[derive(Debug)]
enum JsonKey {
    BuildSteps,
    ExecutableDir,
}

fn get_data_from_json(path: String, key: JsonKey) -> Result<Vec<String>, Box<dyn Error>> {
    let file_path = Path::new(&path);
    let file = File::open(&file_path)?;
    let reader = BufReader::new(file);
    let json: Value = serde_json::from_reader(reader)?;

    match key {
        JsonKey::BuildSteps => {
            // Extract the install steps
            let steps = json["build_steps"]
                .as_array()
                .ok_or("build_steps is not an array")?
                .iter()
                .map(|step| {
                    step.as_str()
                        .ok_or("step is not a string")
                        .map(|s| s.to_string())
                })
                .collect::<Result<Vec<String>, _>>()?;
            Ok(steps)
        }
        JsonKey::ExecutableDir => {
            let execdir = json["executable_dir"].as_str()
                .ok_or("Executable dir not found in json")?;
            Ok(vec![execdir.to_string()])
        }
    }
}

L172 should be moved to another function as it is a helper function—something such as helpers.rs or similar.