shakkar23/shaktrislib — reverse-engineered prompt

I want a small reusable C++ library that implements the core logic for Shaktris or StakTris so I can drop it into another project as a submodule. It should build cleanly with CMake and modern C++ features, and I should be able to add the repo with add_subdirectory and link against it without extra setup.

Please focus on the gameplay engine, not a UI. I want the library to expose headers from the source folder and include a fast board representation using bit operations, solid move generation, and random piece generation with an LCG so it feels lightweight and efficient. Keep the code organized enough that another app can include only the pieces it needs.

If anything is missing, finish the library in the same style as the rest of the repo and make sure it compiles with current g++ or clang versions that support modern C++. A tiny usage example or simple sanity check would help me verify integration. You can look up current docs online if needed.