csplit: avoid negate-with-overflow on an i32::MIN regex line offset

[leeewee]

Fixes #13751

A csplit regex pattern may carry a signed line offset — /regex/OFFSET
or %regex%OFFSET — parsed into an i32. For a negative offset,
do_to_match computed -offset as usize. When OFFSET is i32::MIN
(-2147483648), the negation has no positive i32 counterpart and
overflows, panicking with attempt to negate with overflow under
overflow-checks (exit 134). GNU csplit rejects the offset gracefully.

Fix

Use offset.unsigned_abs(), which yields the magnitude of i32::MIN
without overflowing. The out-of-range offset then produces the normal
line number out of range error, matching GNU (and uutils' own default
release build).

Test

Adds test_up_to_match_negative_offset_min_i32 and
test_skip_to_match_negative_offset_min_i32, covering both the /regex/
and %regex% offset forms. They panic before the fix (the test build has
overflow-checks enabled) and pass after.

[codspeed-hq]

Merging this PR will degrade performance by 18.29%

⚠️ 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
✅ 346 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	571.4 µs	699.4 µs	-18.29%

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 leeewee:csplit-fix-offset-negate-overflow (0c44621) with main (21d4e96)}

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/cut/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/retry (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/cut/mb-non-utf8 is no longer failing!
Congrats! The gnu test tests/mv/mv-exchange is no longer failing!
Congrats! The gnu test tests/od/od-j is no longer failing!
Congrats! The gnu test tests/dd/no-allocate is now passing!
Note: The gnu test tests/misc/write-errors was skipped on 'main' but is now failing.