Preserve header order with per-request emulation

[Joseph-Mutua]

Summary

• preserve client-defined header ordering when applying per-request emulation
• keep explicit request headers overriding emulation defaults
• add deterministic regression coverage for the affected combination

What was happening

Per-request emulation replaces the request's original-header ordering, so a custom order configured on the client was lost. The wrapper now retains the explicit client order and merges it ahead of the selected request emulation's order.

Testing

• bundle exec rake compile
• bundle exec ruby -Itest test/client_test.rb
• bundle exec rake test
• reran the issue reproduction against tls.peet.ws and verified all five cases

Fixes #1

[Joseph-Mutua]

Evidence for the issue reproduction and verification:

• Before/after behavior matrix
• Pre-fix regression failure
• Post-fix verification results
• Complete evidence bundle

[Joseph-Mutua]

@zyc9012 @moya1295 you can verify if this is adequate to close the issue. Any questions/requests welcome

[Joseph-Mutua]

Hi @zyc9012 @moya1295, I’ve rebased this onto the current main branch and resolved the changes introduced since the PR was opened. I also narrowed the regression test so it only checks the reported header-ordering behavior.

Local verification passes:

• native extension compilation
• focused client tests: 12 tests, 38 assertions
• full suite: 59 tests, 172 assertions
• Rust test: 1 passed

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