VecVecDMatch constructor
      
      VecVecDMatch([ 
    
    
- int length = 0
Implementation
factory VecVecDMatch([int length = 0]) => VecVecDMatch.fromPointer(
  ccore.std_VecVecDMatch_new(length),
  externalSize: length * ffi.sizeOf<cvg.VecDMatch>(), // TODO: this is not accurate
);