APP-21128 send telemetry as JSON

[clavi-bot]

Summary

• Send telemetry properties as a JSON request body instead of query parameters.
• Add Content-Type: application/json on SDK requests while preserving the configured endpoint URL exactly.
• Remove the now-unused query encoding helpers and update the README behavior note.

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-app21128 -DSCARF_CPP_BUILD_TESTS=ON
• cmake --build build-app21128 --parallel
• ctest --test-dir build-app21128 --output-on-failure
• cmake --install build-app21128 --prefix /tmp/scarf-cpp-install-app21128
• Downstream find_package(scarf-cpp CONFIG REQUIRED) consumer configure/build with CXX=/usr/local/opt/gcc/bin/g++-15

Linear: APP-21128

[aviaviavi]

Reviewed the current diff, PR metadata, CI status, and existing review discussion. The change correctly moves telemetry properties from query parameters into a JSON request body, preserves the configured endpoint URL, sets Content-Type: application/json, and keeps tests aligned with the new behavior. CI is green and local configure/build/test passed for me as well.

AI-generated review disclaimer: this review was generated by Codex using the GPT-5 Codex desktop harness.