[flake8-simplify] Implement fix for maxsplit without separator (SIM905)

[RazerM]

Stacked on top of #19849; diff will include that PR until it is merged.

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Summary

As part of #19849, I noticed this fix could be implemented.

Test Plan

Tests added based on CPython behaviour.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[MichaReiser]

Could you rebase your PR now that #19849 is merged. It will make it easier for us to review your changes. Thank you

[ntBre]

Thanks, this makes sense to me!

If we wanted to be conservative we could probably gate this behind preview since it's conceptually close to adding a new safe fix to a stable rule. However, I think it's okay because the fact that the fix was missing before was kind of surprising. And there are no changes in the ecosystem either.

[ntBre]

The more I think about this, the more I'm leaning towards using preview to be safe. @MichaReiser do you feel strongly one way or the other? I only found 99 results in a code search, so maybe it's quite a niche pattern anyway.

The preview-gate itself would be easy enough, but we also need a new function in preview.rs and to add the test case to the flake8-simplify preview_rules function, if we go that route.

[MichaReiser]

I think we have to, according to our versioning policy. See #8074 why we might want to change that.

[ntBre]

Sounds good, @RazerM do you mind gating this behind preview?

[RazerM]

@ntBre I think I've done it correctly, but let me know.

[ntBre]

Excellent, thank you!