Align function construction and metadata controls - #9717

Summary

Align function construction and public metadata controls with Python 3.15 in one production Rust file (+209/-68).

• Reuse the shared ArgSpec binder before validating supplied objects. Accept code/globals keywords, retain raw argument owners, and match closure/default/kwdefault validation order and constructor audit veto.
• Emit public code/default/kwdefault read and mutation audits with the correct payloads and None-as-delete behavior. Read live fields after hooks and propagate vetoes before changes. Keep internal defaults accessors unaudited and release all locks before hooks or finalizers.
• Match code/name/type-parameter setter diagnostics, using the live function name after audit. Preserve lone-surrogate names in function repr and closure-count errors without invoking string-subclass formatting callbacks.
• Initialize doc only from a string first constant when the code declares a docstring. Preserve existing metadata identity, version invalidation and release-outside-lock behavior.

No handwritten per-function argument parser, tests, Lib, markers or workflow changes. Existing bound-method and annotation changes remain outside this patch.

Validation

Compared with pinned CPython function controls and its generated Clinic signature. Independent source review passed, including owner lifetimes, audit timing/payloads, lock boundaries and unaudited internal callers.

Reference probes passed 71 metadata cases, four doc initialization cases, 1,024 positional/keyword layouts compared with the shared binder model, and 27 additional metadata/Unicode/hook cases. Constructed or modified code/functions were only inspected, never executed. These are CPython/source checks, not a RustPython runtime pass.

Limits and integration

Old code ownership remains deferred by the existing swap_to_temporary_refs mechanism. CPython releases old code constants earlier, but changing that here would undermine the outstanding-borrow safety design; no immediate-destruction parity is claimed. Shared unexpected-keyword surrogate formatting also remains unchanged. Function deallocation/GC redesign, JIT behavior and annotation reentrancy are outside scope.

Fresh relevant PR patches were checked and do not duplicate this group. Composing #9715 has one textual conflict in function.rs imports: retain this patch's PyDict/PyTypeRef imports and remove PyList once its custom method directory is removed. Independent read-only apply checks confirmed all other hunks apply after that import-only resolution. Combined branches were not compiled or executed. Preserve #9700 annotation diagnostics; that region is unchanged here. #6894 changes freevar representation, and #8624 has adjacent JIT invalidation work that requires preserving its logic if integrated. No combined runtime claim is made.

Native RustPython execution, full workspace/C-API suites and separate cross-platform graphs remain unperformed. Hosted CI is required.

AI-assisted implementation and independent review using OpenAI Codex; model version is not exposed.

Final validation: threaded host-env/VM/stdlib cargo check passed in 1m26s and all-targets Clippy in 3m00s. All 12 existing baseline diagnostics match exactly. Normal repository commit hooks passed; no suppression or unrelated baseline changes.