This is a major release that is focused around code clean-up and modernization.
Much of the work was around removing deprecated and broken components, while updating code to remove usage of deprecated things from Python and ETS. In particular, this release drops support for Python versions 3.5 and earlier.
Additionally, the scimath.units.plugin sub-package has been removed: it was broken and removing it permitted a simplification of dependencies: we don't require Envisage and its dependencies in this release.
See the changelog for a full list of changes included in this release.