Drop unused dependencies cached_property and importlib_resources

[Zac-HD]

I recently noticed that orbax-checkpoint depends on the cached-property package and importlib-resources backport, and wanted to suggest using the standard library instead (respectively @functools.cached_property in Python 3.8+ and the importlib.resources module in Python 3.7+; and note that Python 3.7 is end-of-life next week).

But then when I did a quick search to check how much work this would be... it looks like orbax-checkpoint literally doesn't use these packages at all. So dropping them should be quite trivial, and allow for somewhat smaller virtual environments 😁

[cpgaffney1]

Thanks for pointing this out! importlib_resources is needed by our etils import - for some reason it doesn't get included automatically. The cached_property dependency does seem unneeded though.

[Zac-HD]

Looking at https://github.com/google/etils/blob/4a042b574ddcb6be0e0787539962f874535fb508/pyproject.toml, etils only has optional dependencies, so orbax-checkpoint should depend on etils[epath,epy] rather than plain etils + importlib_resources.

That way we'll automatically stop depending on the backport when etils drops it or makes it version-specific 🙂

[cpgaffney1]

Ah ok thanks, that works! Sending a change now.