Python upgrades

[johnsekar]

Python 3.8+ introduces a lot of new inbuilt features that we currently have to import externally for lower Python versions.
(List will be updated as more features are identified)
(1) functools.cache and functools.cached_property to simplify memoization. https://docs.python.org/3/library/functools.html

[jonrkarr]

If you're going to upgrade, if would make sense to skip to 3.9