Sep. 2025 release

[arporter]

There have been a few additions since the last release (Nov. '24) and, since we planning a PSyclone release, it would be good to get a release of fparser with these in.

They are all small updates/bug fixes although there is a change to the way backslashes in strings are handled. I could argue either way for a bump to either the micro or minor version number.

[hiker]

For Wolfgang: any chance for fixing #428? I could try to have a look, but atm trying to update the PSyclone training is priority (though I am getting close)