APP-21126 add initial C++ SDK

[clavi-bot]

Summary

• add the initial C++17 Scarf SDK with scarf::EventLogger
• support ergonomic custom telemetry properties with type-safe scalar/list/object values
• add env opt-out/verbose handling, default timeout, Scarf-style User-Agent, injectable test transport, and libcurl production transport
• add CMake install/package support, README setup/validation docs, an example, formatting config, and no-network unit tests

Validation

• PATH="/usr/local/opt/llvm@20/bin:$PATH" /usr/local/bin/treefmt CMakeLists.txt include/scarf/event_logger.hpp src/event_logger.cpp src/curl_transport.cpp tests/event_logger_test.cpp examples/basic.cpp README.md .github/workflows/ci.yml treefmt.toml .clang-format
• CXX=/usr/local/opt/gcc/bin/g++-15 cmake -S . -B build -DSCARF_CPP_BUILD_TESTS=ON
• cmake --build build --parallel
• ctest --test-dir build --output-on-failure
• cmake --install build --prefix /tmp/scarf-cpp-install
• configured and built a tiny downstream find_package(scarf-cpp CONFIG REQUIRED) consumer against /tmp/scarf-cpp-install

Notes: local Apple clang/CLT on this host is missing standard library headers (fatal error: 'chrono' file not found), so local validation used Homebrew GCC 15. The GitHub Actions matrix covers Ubuntu, macOS, and Windows with the platform toolchains.

Linear: APP-21126

[aviaviavi]

Reviewed the current diff, PR description, prior discussion state, and CI for this initial C++ SDK. The API, request construction, opt-out handling, libcurl transport, CMake install/export path, README, and no-network tests look sound for this initial release.

Validation checked during review:

• GitHub Actions CI completed successfully on the head commit.
• Built and ran ctest locally from a scratch clone.
• Installed the package locally and built a tiny downstream find_package(scarf-cpp CONFIG REQUIRED) consumer against the installed config.

I did not find any blocking correctness, security/privacy, data handling, packaging, or test coverage issues in the current PR.

AI-generated review by Codex in the Codex desktop harness using GPT-5.