v1.1.6: Unified CMake build with nanobench benchmarks

v1.1.6 — Unified CMake build with nanobench benchmarks

🏗️ Build System

• Unify library, tests, examples, benchmarks, standalone and documentation into a single root CMakeLists.txt; remove the all/, standalone/, test/, examples/ and documentation/ subprojects along with bench/CMakeLists.txt, specific.cmake and the cmake/ helper modules
• Add per-component build options: ECGEN_BUILD_TESTS, ECGEN_BUILD_BENCHMARKS, ECGEN_BUILD_STANDALONE, ECGEN_BUILD_DOCS, ECGEN_ENABLE_CLANG_TIDY and ECGEN_ENABLE_COVERAGE
• Declare the installed-package dependency Py2Cpp 1.6.4 in packageProject

⚡ Performance

• Replace Google Benchmark with nanobench (BM_EMK.cpp, BM_set_partition.cpp) — header-only, no BENCHMARK_MAIN, with instruction/branch counters via doNotOptimizeAway
• Prefer a system-installed fmt and avoid recompiling doctest on every CPM build

🐛 Fixes

• Use SPDLOG_FMT_EXTERNAL when a system fmt is found to avoid duplicate symbols
• Tell CPM that fmt is already handled to prevent duplicate target conflicts
• Rework the standalone EcGen demo to use the real emk_comb_gen API with --size / --comb-size options
• Link coverage flags into SPDLOGGER_EXAMPLE and drop an unused #include <vector>

🧪 Tests

• Add a test_installed consumer test that find_package(EcGen) and checks the installed version header

📖 Documentation

• Update the README for the single-root build layout (cmake -B build, ctest --test-dir build)

🔧 Maintenance

• Switch GitHub Actions workflows to the single-root build and drop stale .bak backups

Full Changelog: v1.1.5...v1.1.6