Function run_args 

pub async fn run_args<I, T>(args: I) -> Result<(), CliError>
where
    I: IntoIterator<Item = T>,
    T: Into<OsString>,

Parse args the same way the real binary parses std::env::args_os(), then run the resulting command. Kept separate from run because recovering the interleaved order of send’s repeatable part flags (--text-part/--file-part/--data-part/--media-type) needs the raw ArgMatches, which Cli::parse() alone discards.