Compilation warning on sign-conversion in the comms library

[TimonTerBraak]

During compilation with the sign-conversion warning flag enables yields the following warning:

include/comms/field/basic/ArrayList.h:676:49: warning: conversion to ‘__gnu_cxx::__normal_iterator<unsigned char*, std::vector<unsigned char> >::difference_type’ {aka ‘long int’} from ‘long unsigned int’ may change the sign of the result [-Wsign-conversion]
  676 |         comms::util::assign(value(), iter, iter + std::min(len, comms::util::maxSizeOf(value())));

I found this while trying to harden my code base (MISRA 2023). I know it is a detail and likely low priority, but I just wanted to file this issue.

[arobenko]

Thanks, I'll try to add explicit cast next release.