shred: support character and block devices

[gabrielhnf]

Fixes #12282 and #12283

shred was rejecting character and block devices with "not a file" error, and doing nothing on them even when they were valid targets. wipe_file used path.is_file() to validate the target, which returns false for all non-regular files, including devices. Additionally, the pass sequence was skipped entirely when metadata.len() == 0, which is always the case for devices.

• Replaced path.is_file() with a check that also accepts character and block devices on Unix
• Character devices now use a dedicated write loop that treats ENOSPC as success if no --size argument was given
• Pass sequences are now always built for devices regardless of reported size
• Block device size is now determined by seeking to the end of the file
• --exact is enforced automatically for non-regular files since they have no meaningful block alignment

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/pipe-f2. tests/tail/pipe-f2 is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/expand/bounded-memory is now passing!
Congrats! The gnu test tests/printf/printf-surprise is now passing!

[codspeed-hq]

Merging this PR will degrade performance by 19.55%

⚠️ 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

❌ 1 regressed benchmark
✅ 316 untouched benchmarks
⏩ 46 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Memory	cp_recursive_deep_tree[(120, 4)]	562.5 KB	699.2 KB	-19.55%

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 gabrielhnf:fix-shred-enospc-and-unreadable-files (b0f36b7) with main (6a942ba)}

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. ↩