Align descriptor initialization and abstract controls with Python 3.15 - #9707

Summary

• Initialize classmethod/staticmethod callable metadata in __new__, preserve identity no-ops, and reload the callable after replacement finalizers reenter initialization.
• Dispatch property copies through the actual subtype constructor, including arbitrary return values, and copy the current name after constructor callbacks.
• Match property initialization publication, owner-release, document lookup/error, and name reset/deletion ordering while preserving the existing lock-safe name replacement.
• Share abstract-marker truth/error handling between the three descriptors and _abc; descriptor abstract markers are read-only.

This Python 3.15 compatibility group changes five Rust files (+125/-170). It is independent of #9453's native staticmethod metadata path; its constructor/metadata additions must be preserved when composing. Broad GC ownership work may require integration care around the existing property name lock-release helper.

Validation

• Source comparison against CPython d220409a13b77de7a6c30abe16ea90db01528edc (funcobject.c, descrobject.c, object.c, and _abc.c).
• External CPython 3.15.0 bounded oracle: wrapper constructors, same-callable metadata preservation, reentrant replacement/finalizer ordering, property subtype construction/arbitrary returns, name reset/deletion, partial state and doc errors, abstract truth/errors/read-only behavior, and ABC marker errors passed.
• Independent review of the frozen patch found no source or lifecycle blockers, including incoming-owner retention and release outside locks.
• Threaded cargo check and all-target Clippy passed with no candidate-file diagnostics. Twelve existing diagnostics remain in unchanged host_env/socket.rs (eight), VM POSIX (one), and ElementTree (three); no lint suppressions were added.
• Rustfmt, diff check, and normal commit hooks passed.

Native RustPython runtime execution was not performed because its required safety guard is not verified. No repository tests, markers, or workflow files were changed. Hosted CI remains required.