Add missing #include <chrono> to src/main.cpp which caused MSVC build
failures since high_resolution_clock and duration_cast were used without
the header (GCC/Clang included it transitively). Remove obsolete
appveyor.yml (superseded by GitHub Actions). Add ASAN+UBSAN build
jobs for Linux and macOS in the CI workflow.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
