support typing.Final annotation

[carljm]

Doc: https://docs.python.org/3/library/typing.html#typing.Final
Spec: https://typing.python.org/en/latest/spec/qualifiers.html#uppercase-final

• Infer the type of the RHS for public uses of bare Final symbols
• Add a new diagnostic for modifications of Final-qualified symbols
• Make sure that both of the above also works for attributes
• Disallow Final in function parameter definitions / return-type annotations
• Prevent overriding of Final attributes in subclasses
• Report an error if there is no binding to a Final-qualified symbol
• Variance inference: if an attribute is marked Final, its type should be covariant rather than invariant

Somewhat related tickets: #433, #529

[MichaReiser]

@sharkdp could you update what's left to do in this issue? I think most of it is now handled?

[sharkdp]

could you update what's left to do in this issue?

I kept the checklist in the description very much up to date.

I think most of it is now handled?

I still want to merge astral-sh/ruff#19480 and then I was planning to close this and write follow-up tickets. I think "Prevent overriding of Final attributes in subclasses" is also a core aspect of Final, but that could probably be done when we tackle Liskov enforcement, which I think would set up the required functionality anyway(?).