fix: correctly support multiValueHeaders in rust functions during development

[danez]

Summary

multiValueHeaders was simply not forwarded from the response of the rust function

This is similar to #4618 but for rust.

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[github-actions]

📊 Benchmark results

Comparing with a8bfc66

Package size: 287 MB

⬇️ 0.00% decrease vs. a8bfc66

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• T-30 (a8bfc66): 287 MB
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• T-10 (f5b1ab5): 286 MB
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• T-2 (d35f7e0): 285 MB
• T-1 (f4ee7a4): 285 MB
• T (current commit): 287 MB