Use Java streams on SQL fetches effectively

[sebastian-peter]

Once #773 is merged:

The call to stream() here does not make much sense if one thinks of why we want to use it in the first place. We fetch all rows for a query first, then apply a stream on it to "lazily" handle the rows one by one. We definitely should not handle this in this PR though, I think. I found information on how to do it though: https://stackoverflow.com/a/64391247

Originally posted by @sebastian-peter in https://github.com/ie3-institute/PowerSystemDataModel/pull/773#discussion_r1205376824