Parsing: avoid initializing the header array before parsing

[Tpt]

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[codspeed-hq]

Merging this PR will improve performance by 21.81%

⚠️ 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 improved benchmarks
✅ 1 untouched benchmark

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	client_server_no_body	140.4 µs	113.4 µs	+23.78%
⚡	client_server_fixed_body	158.5 µs	132.2 µs	+19.88%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing headers-init (fd1e2a9) with main (431b3bb)}