Function label_number 

pub fn label_number(
    accuracy: Option<f64>,
    prefix: &str,
    suffix: &str,
    scale: f64,
) -> impl Fn(f64) -> String + Send + Sync

General configurable number formatter (R’s scales::label_number). Multiplies by scale, rounds to accuracy (None = trim), groups thousands with ,, and wraps in prefix/suffix — with the minus sign placed before the prefix (-€5). For a custom thousands mark use label_currency.