benchmark: pass timeout to stream.write

[mbeijen]

Without it, send() drains the payload in one call and the buffer-slicing loop never iterates.

This is the reason our benchmark does not show an improvement for #954

[codspeed-hq]

Merging this PR will degrade performance by 99.79%

❌ 1 regressed benchmark
✅ 6 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	test_bench_sync_stream_write_large	242.1 ms	114,880.9 ms	-99.79%

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 mbeijen:perf/benchmark-add-timeout (3d8f25c) with main (c1d3d95)}