ci: reject implicit engine buffer allocation

[gatesn]

Summary

Reject implicit buffer allocation in engine code.

Changes

• Add a check for implicit constructors in allocator-aware paths.
• Run the check in Rust lint CI.

[codspeed-hq]

Merging this PR will degrade performance by 27.52%

⚠️ 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.

❌ 2 regressed benchmarks
✅ 2092 untouched benchmarks
⏩ 206 skipped benchmarks¹

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]	12.2 µs	20.4 µs	-40.29%
❌	WallTime	words_gather_scalar_avx2[65536]	8.2 µs	9.4 µs	-12.01%

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 ngates/buffer-allocator-enforce (c18fde8) with ngates/buffer-allocator-execution (a8ffb77)}

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. ↩