Function run_diff_multi 

pub fn run_diff_multi(
    baseline_path: PathBuf,
    target_paths: Vec<PathBuf>,
    output: ReportFormat,
    output_file: Option<PathBuf>,
    fuzzy_preset: String,
    include_unchanged: bool,
    graph_diff: bool,
) -> Result<()>

Run the diff-multi command (1:N comparison)