gh-61103: use PEP 3118 codes in the ctypes

[skirpichev]

This change only buffer protocol support for complex types, _type_ properties aren't affected.

• Issue: Add support for C99 complex type (_Complex) as ctypes.c_complex #61103

[skirpichev]

@encukou, I think this should fix compatibility with NumPy (buffer protocol). We can decide later what to do with _type_ (use same code or not).

[encukou]

I'm worried that this is a breaking change relative to Python 3.14.
It should definitely be mentioned in What's New if it gets in.

But, with #148676 this would be redundant.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #32526288 | 📁 Comparing 7aa47c3 against main (2ba0a81)

  🔍 Preview build  

10 files changed · ± 10 modified

± Modified

• deprecations/index.html
• deprecations/pending-removal-in-3.19.html
• library/calendar.html
• library/http.cookies.html
• whatsnew/3.12.html
• whatsnew/3.13.html
• whatsnew/3.14.html
• whatsnew/3.15.html
• whatsnew/changelog.html
• whatsnew/index.html

[skirpichev]

It should definitely be mentioned in What's New if it gets in.

Done.

But, with #148676 this would be redundant.

(I think merging that pr is a bad idea.)

Though, you are right, my 3 PRs - only an alternative.

[vstinner]

I merged my PR instead which changes ctypes _type_. This change would be an alternative if we decide later to leave _type_ unchanged and only change the used buffer format.