printf, seq: fix abort on large field width and precision

[eyupcanakman]

printf and seq abort with SIGABRT on a large field width or precision:

printf '%.70000f' 1
printf '%70000d' 1
printf '%500000s' x
seq -f '%.70000f' 1 1

Rust's formatting machinery panics once a dynamic width or precision passes u16::MAX, and the release build turns that panic into an abort. GNU produces the padded output, so these now do too.

While tracing it I found a second bug in the same path. printf '%.1000f' 1 printed 1 instead of 1. and 1000 zeros, because bigdecimal's Display stops padding past 1000 digits. The %f formatter now assembles the digits directly, which fixes both. Padding is written in fixed chunks so a wide field costs no extra memory.

#12620 uses the same chunked-padding approach for the width case. This also handles the large precision and the truncation, which #12620 and #12603 leave unfixed.

seq's own precision detection derives an unbounded value from the exponent text (seq 1e-3000000000 1e-3000000000), which this does not touch. That path is tracked in #13221.

Fixes #12708

[codspeed-hq]

Merging this PR will improve performance by 18.37%

⚠️ 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 improved benchmark
✅ 338 untouched benchmarks
⏩ 46 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	seq_formatted	94.7 ms	80 ms	+18.37%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing eyupcanakman:fix/printf-large-width-precision-panic (76445dd) with main (8894319)}

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. ↩

[sylvestre]

Please fix the job issue