Function install_with_footer 

pub fn install_with_footer<F>(footer: F)
where
    F: Fn() -> String + Send + Sync + 'static,

Install the report handler (if not already) and register a closure that appends a tool-specific support footer to every rendered diagnostic.

footer is called on every diagnostic render and may return an empty string to suppress the footer for that render. Replacing the footer is permitted — the most recent call wins.