split: fix add-overflow in suffix-length calculation

[leeewee]

Fixes #13749

split auto-computes the suffix length from the suffix start value
(--numeric-suffixes=N / --hex-suffixes=N) and the chunk count (-n).
Suffix::from did this as start as u64 + chunks, with no guard against
the sum exceeding u64::MAX. A start near u64::MAX, or a chunk count
near u64::MAX with a nonzero start, overflows the add and panics with
attempt to add with overflow under overflow-checks (exit 134).

Fix

Widen the sum to u128 so it can't overflow. The value only feeds a log
for the digit count, so results are identical for every in-range input,
and the out-of-range case now reports the normal
the suffix length needs to be at least N error instead of aborting —
matching GNU (which accepts such a start only once -a is large enough).

Tests

Adds three regression tests covering both operands and both radixes: a huge
decimal start, a huge hex start, and a huge -n chunk count. Each panics
before the fix (the test build enables overflow-checks) and passes after.

[codspeed-hq]

Merging this PR will degrade performance by 18.31%

⚠️ 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	699.6 µs	-18.31%

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:split-fix-numeric-suffix-add-overflow (383f289) 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. ↩