gh-150942: Speed up FrameLocalsProxy.values()

[catlover-bot]

Summary

Speed up FrameLocalsProxy.values() by using
_PyList_AppendTakeRef() when adding values returned by
framelocalsproxy_getval().

framelocalsproxy_getval() returns a new reference. Previously,
PyList_Append() added another reference to the value and the original
reference was then decremented by the caller.

Using _PyList_AppendTakeRef() transfers the existing reference directly
to the result list, avoiding the unnecessary incref/decref pair while
preserving ownership and error handling.

Benchmarks

Benchmarks used pyperf 2.10.0 with CPython 3.16.0a0 built using
--enable-optimizations --with-lto.

Environment:

• Linux x86-64 on WSL2
• Intel Core i5-1135G7
• GCC 13.3.0
• benchmark process pinned to CPU 2

FrameLocalsProxy.values() microbenchmark

Frames contained ordinary heap objects rather than immortal small
integers.

Locals	Baseline	Patched	Change
8	120 ns	105 ns	1.14x faster
32	337 ns	264 ns	1.27x faster
128	1.13 us	1.03 us	1.10x faster
256	2.23 us	2.01 us	1.11x faster
geometric mean	reference		1.15x faster

An earlier independent run produced a 1.16x geometric-mean speedup.

Tracing/debugger-like workload

A sys.settrace() workload was also tested where the trace function
enumerates frame.f_locals.values() on line events.

Locals	Baseline	Patched	Result
32	68.4 us	69.3 us	not significant
128	127 us	125 us	not significant
256	189 us	181 us	1.04x faster

The improvement is mostly hidden by surrounding tracing overhead in the
smaller workloads, while the 256-local case still shows a measurable
improvement.

Validation

• python -m test test_frame: passed
• python -m test -R 3:3 test_frame: passed
• reference ownership test: passed
• optimized-build semantic smoke test: passed
• git diff --check: passed

AI assistance was used while investigating this issue, designing the
benchmarks, and preparing the change. I reviewed the implementation,
reference ownership semantics, benchmark methodology, and test results
myself.

• Issue: Improve performance by using reference stealing methods #150942

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