gh-150942: Speed up BytesIO.readlines() using reference-stealing append

[Taeknology]

Summary

Use _PyList_AppendTakeRef() while building the private result list in
BytesIO.readlines().

The new bytes object is transferred directly to the result list, avoiding the
incref/decref pair performed by PyList_Append(). The result list is freshly
allocated, remains local for the complete loop, and is protected by the
BytesIO critical section until it is returned.

Partially fixes gh-150942.

Benchmark

Author-run pyperf comparisons used five BytesIO.readlines() workloads on a
free-threaded Clang 21 PGO+ThinLTO build. Two balanced baseline/patch comparison
pairs reported improvements of 8.64% to 36.18% across the workloads, with
19.27% and 20.43% equal-weight geometric-mean improvements. Earlier regular-GIL
PGO+LTO comparisons reported 7.64% and 8.68% geometric-mean improvements.

Several individual suites produced pyperf check stability warnings. The raw
benchmark script and result files are not attached to this PR, so these figures
are author-reported results and are not independently reproducible from the
public PR artifacts.

Verification

All required GitHub checks pass on the current head, including regular and
free-threaded builds and tests, sanitizer jobs, and generated-file checks.
git diff --check also passes for the complete two-file diff.