Function newer_time_span_for_config 

fn newer_time_span_for_config(
    cur_span: Option<Duration>,
    config_name: &str,
    config_span: &str,
) -> CargoResult<Option<Duration>>

Returns the shorter duration from cur_span versus config_span.

This is used because the user may specify multiple options which overlap, and this will pick whichever one is shorter.

• cur_span is the span we are comparing against (the value from the CLI option). If None, just returns the config duration.
• config_name is the name of the config option the span is loaded from.
• config_span is the span value loaded from config.