Improved error messages. SDAPI exceptions are now mostly wrapped in a ZgyError exception, allowing OpenZGY to substitute a more readable message in the (regrettably few) cases it can do so.

Add code to re-open the last segment in a cloud file. Add unit tests for update on cloud both at the FileADT level and at the IZgyWriter level.

Honor "iothreads" when reading from seismic store, allowing OpenZGY to do more parallelizing internally.

Make LocalFileLinux::xx_readv() honor the request for parallel delivery. But don't use the feature yet.

Yagni: Remove the Config class and derivatives. Meant to be an internal version of IOContext but was never fully used in the C++ version. Might potentially be brought back and used later.