v0.5.4: Supporting MSVC on Windows 🪟

The less_slow.cpp project now supports Microsoft Visual C++ (MSVC), thanks to the extensive list of patches suggested by @RazielXYZ 👏

Key updates include switching to OpenBLAS via FetchContent for comparable linear algebra performance across platforms, enabling OpenMP on MSVC for parallelism in Eigen-based computations, and revising OpenMP loop indices to use int64_t, as MSVC requires signed types for parallel loops. The detection of physical cores on high-core-count Windows systems has also been improved by implementing GetActiveProcessorCount(ALL_PROCESSOR_GROUPS) and refining physical core detection logic. Furthermore, the integration addresses missing functionality, such as the lack of __builtin_popcountll on MSVC, with a manual fallback for is_power_of_two.

Additional findings include MSVC-specific behaviors, such as how linking AVX-512 code significantly slows down builds and how assembly-based benchmarks require further investigation for proper MSVC integration. Interestingly, heavily-templated libraries, like Ranges-v3 or CRTE (Compile-time RegEx), show much worse performance on MSVC than with GCC and Clang.