pub fn write_toml(
        &self,
        options: &HakariOutputOptions,
        out: impl fmt::Write,
    ) -> Result<(), TomlOutError> {
        write_toml(&self.builder, &self.output_map, options, out)
    }
Writes `[dependencies]` and other `Cargo.toml` lines to the given `fmt::Write` instance.

`&mut String` and `fmt::Formatter` both implement `fmt::Write`.
tools/hakari/src/hakari.rs