[codex] Add smoke marshalling benchmarks

[anthonyprintup]

Summary

• add opt-in Google Benchmark smoke targets for Protocyte marshalling and protobuf comparison
• extract shared UltimateComplexMessage fixture setup for smoke tests and benchmarks
• generate a protobuf-only benchmark schema without Protocyte extensions
• ensure the protobuf benchmark fetches a linkable protobuf runtime when only standalone protoc is available

Validation

• clang-format on touched C++ files
• cmake --build smoke\build\clangcl --target protocyte_host_smoke
• cmake --build smoke\build\clangcl-benchmarks --target protocyte_host_benchmark protocyte_host_protobuf_benchmark
• ctest --test-dir smoke\build\clangcl --output-on-failure (25/25 passed)
• short smoke runs for protocyte_host_benchmark and protocyte_host_protobuf_benchmark
• reproduced the protoc-only benchmark configure case and verified the fallback fetch path now configures and builds protocyte_host_protobuf_benchmark
• git diff --check

[anthonyprintup]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Another round soon, please!

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