cosmo: properly annotate method overrides - #18802

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@eerovaher, this relates to #18360. Do you think I should merge this PR into that one, as part of the conversation around having typing_extensions ?

typing.override is in the standard library starting from Python 3.12, so if we drop support for Python 3.11 then we will not need typing_extensions for this feature.

So if we're not dropping 3.11 for a year you'd be in favour of adding typing_extensions ?

I have no intention of waiting a year before dropping support for Python 3.11. With typing_extensions we can use some of the later typing features in Python 3.11, but PEP 695 – Type Parameter Syntax cannot be provided by a library.

It very well might be a while before py3.11 is dropped. If we remain compatible with numpy for 1 year past its SPEC0 dates then...

Regardless, typing_extensions is required right now, for this PR. If we get to remove it as a dependency by the time Astropy v8 is released, no harm no foul? If it turns out we need it, then we need it. It's all a question of our threshold for adding dependencies. Like packaging, for nearly-core-Python batteries-included packages, that threshold is low.

It very well might be a while before py3.11 is dropped.

That's defeatist.

That's pragmatic and optimistic. It's finding solutions given current constraints while ensuring that those solutions don't prevent more optimal solutions when constraints are removed.

1. ✅ Finding a solution given constraints: we don't have py3.12+ but with typing_extensions we can easily accomplish our goals of improved type annotations.
2. ✅ ensuring that those solutions don't prevent the optimal solutions. typing_extensions -> typing couldn't be more trivial, when we do transition to py3.12+. Moreover, build(deps): typing-extensions as a dependency #18360 can be accomplished concurrently with efforts to drop py3.11. ruff UP035 seamlessly handles any transition, including bug-fix backports.

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