Speculative major release, with some potentially breaking changes to clear some technical debt. Things to review include:

• Modern packaging, including removal of setup.cfg
• remove EOL Python versions (minimum version of 3.7? higher?) as tests are failing to conform more frequently to older versions for benign reasons
• tidy source tree with black or ruff
• review some of the core logic that probably could be simplified, was based on Python 2 string handling
• revalidate if some of the unusual data structures to support Jython are still fit for purpose