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 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.

⚡ 5 improved benchmarks
❌ 1 regressed benchmark
✅ 217 untouched benchmarks
⏩ 2028 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	compress[(10000, 4)]	496.8 µs	614.3 µs	-19.13%
⚡	Simulation	decompress[u64, (4000, 1024)]	89.5 µs	71.5 µs	+25.23%
⚡	Simulation	take_indices[(1000, 4)]	110.4 µs	95.3 µs	+15.9%
⚡	Simulation	take_indices[(4000, 256)]	100.9 µs	89.6 µs	+12.64%
⚡	Simulation	decompress[u16, (4000, 1024)]	60.2 µs	54.1 µs	+11.39%
⚡	Simulation	decompress[u8, (10000, 4)]	218.3 µs	197.2 µs	+10.73%

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 (13894b2) with ngates/buffer-allocator-execution (6931802)²}

Footnotes

1. 2028 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. No successful run was found on ngates/buffer-allocator-execution (3c868b7) during the generation of this report, so 6e251f7 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩