head: don't panic on a write error while printing a verbose header

[leeewee]

Fixes #13264

The verbose ==> name <== header wrote the filename with print_verbatim(file).unwrap(), while the surrounding header writes use ?. When the filename is longer than the stdout buffer (~1024 bytes), write_all flushes mid-write, so a write error (e.g. stdout on a full device) is raised inside the unwrap and aborts the process instead of being reported.

This propagates the error with ? like the neighbouring writes, so a write failure exits non-zero with a message instead of panicking, regardless of filename length.

Before:

$ LONG="/dev/$(python3 -c "print('./'*512)")null"
$ head -v "$LONG" > /dev/full
thread 'main' panicked at src/uu/head/src/head.rs:463:42:
called `Result::unwrap()` on an `Err` value: Os { code: 28, kind: StorageFull, message: "No space left on device" }
Aborted (core dumped)          # exit 134

After (consistent with the short-filename path, and non-zero like GNU):

$ head -v "$LONG" > /dev/full ; echo $?
head: No space left on device
1

A regression test (test_verbose_header_long_name_write_error_no_panic) covers it with .fails_with_code(1), which the pre-fix abort would not satisfy.

[github-actions]

GNU testsuite comparison:

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

[codspeed-hq]

Merging this PR will improve performance by 4.85%

⚡ 1 improved benchmark
✅ 330 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	sort_ascii_utf8_locale	16.1 ms	15.4 ms	+4.85%

Tip

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_{Comparing leeewee:head-fix-verbose-header-write-unwrap (2a9b4ea) with main (2a92fcc)}

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. ↩