rasmusbarr/nudge ? reverse-engineered prompt

Build me a small 3D rigid body physics library in C that focuses on being fast and data oriented.

I want the core to handle basic rigid body simulation for things like gravity, motion, collisions, and impulses, with a simple API I can call from a sample app. Please include a working example and a few tests so I can see it running and verify the basics.

If it makes sense, optimize for SIMD friendly code, but make sure it still builds cleanly on machines that do not support AVX2 or FMA. If you need to, look up the current docs online so the build settings are sensible on common tools like Xcode or Visual Studio.

Keep it lightweight and practical, with the main goal being a small physics library that is easy to understand and use.