gh-125196: Use PyUnicodeWriter for repr(tuple)

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• Issue: Use the public PyUnicodeWriter API #125196

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Benchmark:

import pyperf runner = pyperf.Runner() runner.bench_func('repr(())', repr, ()) runner.bench_func("repr(('abc',))", repr, ('abc',)) runner.bench_func('repr((1,2,3))', repr, (1, 2, 3)) tuple4 = ('abcdef',) * 10 runner.bench_func('repr(tuple4)', repr, tuple4) tuple5 = ('abcdef',) * 50 runner.bench_func('repr(tuple5)', repr, tuple5) 

Result on Python built with ./configure CC=clang LD=clang --with-lto=thin, CPU isolation, benchmark run with --rigorous:

+----------------+---------+-----------------------+ | Benchmark | main | change | +================+=========+=======================+ | repr(()) | 55.0 ns | 55.9 ns: 1.02x slower | +----------------+---------+-----------------------+ | repr(('abc',)) | 210 ns | 239 ns: 1.14x slower | +----------------+---------+-----------------------+ | repr((1,2,3)) | 290 ns | 189 ns: 1.54x faster | +----------------+---------+-----------------------+ | repr(tuple4) | 850 ns | 870 ns: 1.02x slower | +----------------+---------+-----------------------+ | Geometric mean | (ref) | 1.05x faster | +----------------+---------+-----------------------+ Benchmark hidden because not significant (1): repr(tuple5)