PyQt5 -> PySide6 update on github

[Steve Ludtke]

EMAN2 has used PyQt since we started development 20 years ago. Maybe a decade ago we updated from PyQt4 to PyQt5. I just completed the trasition of all (I hope) code to PySide6 (this is the "official" equivalent of PyQt6). While I've tested it fairly extensively, Qt6 changes how OpenGL works pretty significantly, so there may be some issues on specific machines. If you have problems, please report them!

The binaries have not been updated yet, but master on GitHub has, so if you do a git pull with a make install, you will get the new version. If you have serious issues, just rewind your git checkout to before July 10, 2026 and report the problem. Once we've dealt with any major issues, we'll do a corresponding binary release.