matplotlib dropped support for the Qt4Agg backend since Qt4 reached EOL back in 2015, so hypertools's backend management code now throws a ValueError when checking whether it's available, which we weren't expecting and therefore isn't caught.
matplotlib now supports Qt5 and Qt6, but has also combined them into a single "QtAgg" backend rather than separate them by version
need to:
remove Qt4Agg from the set of backends checked here
update the set of standard backends checked to reflect those matplotlib currently supports, listed here
handle ValueError here to deal with this properly in the future
matplotlib dropped support for the Qt4Agg backend since Qt4 reached EOL back in 2015, so hypertools's backend management code now throws a ValueError when checking whether it's available, which we weren't expecting and therefore isn't caught.
matplotlib now supports Qt5 and Qt6, but has also combined them into a single "QtAgg" backend rather than separate them by version
need to: