feat: Implement BufWriter optimization for du stdout output (fixes #9…

[naoNao89]

Replace direct print! statements with 64KiB buffered writes to reduce syscall overhead for du -a on large directories. This addresses the performance issue where each file entry triggers multiple stdout writes.

Changes:

• Add BufWriter field to StatPrinter struct with 64KB buffer
• Convert print_stat method to use buffered writes instead of direct output
• Add Drop implementation to ensure proper buffer flushing
• Add comprehensive benchmarks to validate performance improvement

Performance: Reduces syscalls from ~16,500 to ~3-5 for 5,500 file directories, providing significant improvement for the issue #9146 use case.

Re-open: #9163

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will improve performance by 10.45%

_{Comparing naoNao89:feature/du-buffer-optimization-9146 (4715083) with main (1fbd765)}

Summary

⚡ 1 improved benchmark
✅ 141 untouched benchmarks
🆕 2 new benchmarks
⏩ 180 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
🆕	Simulation	du_all_stress_balanced_tree[(3, 5, 6)]	N/A	1.2 ms	N/A
⚡	Simulation	du_all_wide_tree[(5000, 500)]	19.3 ms	17.5 ms	+10.45%
🆕	Simulation	du_all_extreme_wide_tree[(2000, 500)]	N/A	10.3 ms	N/A

Footnotes

1. 180 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/du/inodes. tests/du/inodes is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/overlay-headers (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/overlay-headers (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)