randuAsync function
RandU Generates a single uniformly-distributed random number or an array of random numbers.
For further details, please see: https://docs.opencv.org/master/d2/de8/group__core__array.html#ga1ba1026dca0807b27057ba6a49d258c0
Implementation
Future<Mat> randuAsync(InputOutputArray dst, Scalar low, Scalar high) async {
  return cvRunAsync0((callback) => ccore.cv_randu(dst.ref, low.ref, high.ref, callback), (c) {
    return c.complete(dst);
  });
}