Function install_single_binary 

pub async fn install_single_binary(
    client: &Client,
    dirs: &Dirs,
    tool: &str,
    version: &str,
    urls: &[String],
    exe_name: &str,
    download_name: &str,
    os: Os,
    checksum: Option<&Checksum>,
    show_progress: bool,
    offline: bool,
    require_checksums: bool,
    attestation: Option<&GithubAttestation>,
) -> Result<()>

Download a single executable into <install>/bin/<exe_name> and mark the install complete. Tries each URL in order (failover), optionally verifying a checksum. Used for standalone binaries (e.g. github: bare binaries).