- build and run poac cmd on windows
    - add cmake build system
    - add vcpkg package manager

- Refactored `buildImpl` to handle multiple build systems (`Makefile` and `Xmake`).
- Introduced `emitXmakeLua` method to generate Xmake-specific build files.
- Added `--build-system` option to `build` command for selecting the desired build system.
- Fixed improper handling of file descriptors in `Command` class on Windows.

- corrected the `waitpid` function in `Command` class to use the `process` member properly.
- updated `Child::waitWithOutput` to align return fields with consistent naming (`stdout_str` and `stderr_str`).

- introduced a testing framework with test targets for core components.
- separated `poac` into a library (`poac_lib`) and executable for modularity.
- add support for stricter compiler diagnostics and warnings on supported platforms.
- updated CMake presets to simplify and unify build configurations for Ninja and Visual Studio.
- refined `CMakeLists.txt` to include `clang++` as the default compiler on Unix if available.