feat(zend): add response header wrappers

[ptondereau]

Description

Add zend::set_header, add_header, remove_header, remove_all_headers and set_response_code, safe wrappers around sapi_header_op that only fill line/line_len of a zeroed sapi_header_line and use the bindgen op constants, so the 8.5 union and the shifted SAPI_HEADER_* values need no cfg. They refuse to run outside a request (the header list only lives between sapi_activate and sapi_deactivate_module) and while a SapiGlobals guard is alive, since the engine rewrites SG(sapi_headers) under it.

Checklist

• I have read the contribution guidelines and the code of conduct.
• I have added tests that prove my code works as expected.
• I have added documentation if applicable.
• I have added a migration guide if applicable.

[coveralls]

Coverage Report for CI Build 38048407340

Coverage increased (+0.2%) to 75.064%

Details

• Coverage increased (+0.2%) from the base build.
• Patch coverage: 1 uncovered change across 1 file (98 of 99 lines covered, 98.99%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
src/zend/headers.rs	99	98	98.99%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	14942
Covered Lines:	11216
Line Coverage:	75.06%
Coverage Strength:	53.03 hits per line

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💛 - Coveralls

[codspeed]

Merging this PR will not alter performance

⚠️ 51 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• output_transforms[100000]
• object_news[100000]
• exception_throws[100000]
• output_passthroughs[100000]
• property_dumps[100000]
• array_interned_keys[10]
• output_transforms[10]
• output_passthroughs[10]
• array_interned_keys[1]
• object_news[10]
• …and 41 more

✅ 51 untouched benchmarks

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_{Comparing feat/zend-response-headers (705a525) with master (c9a40ce)}