code: func opcodeSize(op *parsedOpcode, vm *Engine) error {
  	so, err := vm.dstack.PeekByteArray(0)
  	if err != nil {
  		return err
  	}
  
  	vm.dstack.PushInt(scriptNum(len(so)))
  	return nil
  }
docs: // opcodeSize pushes the size of the top item of the data stack onto the data
  // stack.
  //
  // Stack transformation: [... x1] -> [... x1 len(x1)]