cp: simplify loop by while let

[oech3]

No description provided.

[codspeed-hq]

Merging this PR will degrade performance by 11.4%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 2 regressed benchmarks
✅ 345 untouched benchmarks
⏩ 46 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	df_with_path	571 µs	699.7 µs	-18.39%
❌	Simulation	cksum_multiple_files	60.6 ms	63 ms	-3.8%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing oech3:cp-loop (348be08) with main (0b214cc)}

Footnotes

1. 46 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:

Skip an intermittent issue tests/tail/retry (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout-group (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/misc/write-errors was skipped on 'main' but is now failing.

[cakebaker]

Thanks!