🧪 Add test for build_http_client

[edithatogo]

🎯 What: The build_http_client function was previously missing tests. Given that causing this function to fail (since its parameters are statically typed and hardcoded with valid defaults) without a complete refactor is essentially impossible under normal test conditions, a happy path test was implemented instead.

📊 Coverage: A happy path test was implemented to ensure build_http_client successfully returns an Ok(reqwest::Client) and does not panic during client builder invocation.

✨ Result: Test coverage improved for the src/hardening.rs module and ensures we catch regressions if build_http_client's underlying configuration changes in a way that would cause build to return an Err.

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PR created automatically by Jules for task 5639685235989652324 started by @edithatogo

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