Function send_at 

pub async fn send_at<const CAP: usize>(
    command: &str,
) -> Result<ArrayString<CAP>, Error>

Send an AT command to the modem.

The const CAP parameter is the size of the returned response string. It is ok to set this to 0 you don’t need the response.

If the CAP is too small to contain the entire response, then the string is simply tuncated.