Fix annotations reader for python 3.14 in PreTrainedModel

[neo]

What does this PR do?

There's an issue in Python 3.14 that __annotations__ is not available anymore because of an implementation change (ref), and it breaks the config retrieving logic.

This fix would use the recommended reader to properly get the annotations.

This is similar to and trying to fix the same issue as #44165, but it should hopefully look and feel less risky.

(I hope this can also be patched back to v4)

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@Rocketknight1 @ArthurZucker @Cyrilvallez @vasqu

[Rocketknight1]

This LGTM, and is a much cleaner fix! It will not work on Python 3.9 or earlier, but these are now EOL and no longer supported, so I think it's okay.

[neo]

Thank you @Rocketknight1! ❤️

I do wonder if we're going to backport this to another v4 release 😳

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[Rocketknight1]

@neo unlikely unfortunately, backports to v4 are generally not happening!