Support mixed decimal multiplication

[onursatici]

Summary

Derive multiplication result types from both decimal operands and accept signed primitive integers without casting input arrays. Execute directly over canonical integer buffers while preserving checked decimal overflow and null semantics.

[codspeed-hq]

Merging this PR will regress 1 benchmark

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ 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

⚡ 13 improved benchmarks
❌ 1 regressed benchmark
✅ 2076 untouched benchmarks
⏩ 206 skipped benchmarks¹
🗄️ 4 archived benchmarks run²

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	arrow_checked_add_u32_neon[16384]	12.4 µs	20.3 µs	-39.14%
⚡	WallTime	add_shapes_neon[(128, PerRowPerRow)]	3.7 µs	1.9 µs	+88.85%
⚡	WallTime	subtract_shapes_neon[(128, PerRowPerRow)]	2.9 µs	1.9 µs	+50.55%
⚡	WallTime	multiply_shapes_neon[(128, PerRowPerRow)]	2.9 µs	2 µs	+46.75%
⚡	WallTime	arrow_checked_add_u32_avx512[16384]	21.3 µs	17.7 µs	+20.33%
⚡	WallTime	add_u32_nonnull_neon	7.9 µs	6.8 µs	+16.29%
⚡	WallTime	compare_int_nullable_neon	5.6 µs	4.9 µs	+15.87%
⚡	WallTime	compare_int_constant_neon	4.4 µs	3.8 µs	+14.11%
⚡	WallTime	add_shapes_neon[(16384, PerRowPerRow)]	11.3 µs	9.9 µs	+14.07%
⚡	WallTime	add_i32_nonnull_neon	9 µs	7.9 µs	+13.45%
⚡	WallTime	add_i64_nonnull_neon	11.3 µs	10 µs	+13.05%
⚡	Simulation	cold_misaligned[(16, 64)]	392.4 µs	347.3 µs	+13%
⚡	WallTime	compare_int_eq_neon	4.9 µs	4.4 µs	+10.8%
⚡	WallTime	compare_int_neon	4.9 µs	4.4 µs	+10.54%

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 os/decimal-mul (c25e1d9) with develop (a67cd1b)}

Footnotes

1. 206 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. ↩

2. 4 benchmarks were run, but are now archived. If they were deleted in another branch, consider rebasing to remove them from the report. Instead if they were added back, click here to restore them. ↩

[robert3005]

I think we want to expand this to all decimal operations