Optimize PyBytes::as_bytes() in the unlimited API

[exg]

No description provided.

[codspeed-hq]

Merging this PR will degrade performance by 10.49%

⚠️ 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

❌ 2 regressed benchmarks
✅ 139 untouched benchmarks
⏩ 6 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	extract_u128_small	1.8 µs	2.1 µs	-10.62%
❌	Simulation	extract_u128_zero	1.9 µs	2.1 µs	-10.35%

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 exg:optimize-pybytes-as-bytes-in-unlimited-api (f25785e) with main (d44dcca)}

Footnotes

1. 6 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. ↩