Use annotate coordinate systems to simplify label_subplots.

[anntzer]

The ability of annotate to specify various coordinates systems simplifies label_subplots, by avoiding the need to explicitly construct a ScaledTranslation (while maintaining exact functionality parity).

PR summary

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

[anntzer]

Reordered the parameters; also switched to using "offset fontsize" in one of the two examples (thanks @saranti for pointing this out in #25907 (comment)) as that's the more natural unit here.

[QuLogic]

I'm not sure if this would be better in the text above instead of a comment, but unfortunately, the CI-built docs have been garbage-collected now.

[anntzer]

Re-triggered a CI run.

[anntzer]

Should still be good to go.

[jklymak]

I'm fine with this, and feel free to ping for a merge when docs finish.

But, did you consider keeping both in the example? ScaledTranslation is useful for other things, so an intuitive application has some value, even if there is a nicer way to do that application?

[anntzer]

Fair point; I restored the use of ScaledTranslation for the second example (I don't think we need to have both versions for both examples, they are really the same).

[jklymak]

For some reason pre-commit needs to be appeased.

[anntzer]

Oops, sorry misclicked :/ and accidentally merged just after pushing the pre-commit fix. @jklymak let me know if there's anything else you think should be fixed.