Preserve request headers when mutating cache tests

[atomiczsec]

Summary

• clone the original request line, headers, and body before mutating request targets so cache-busting tests work for any method while preserving sensitive headers
• add a helper for the HPP cache-key test to rebuild requests with polluted query strings and bail out cleanly when a request cannot be built
• share the new cloning logic to keep normalization and other cache tests from losing authentication headers while still allowing cookies to be stripped

Testing

• ./gradlew test

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Codex Task