[INFO] building with MacPorts

I managed to run this example by installing dependencies using [MacPorts](https://www.macports.org/) instead of pixi,. Here is what I had to do:

Install deps:
```
sudo port install cmake opencv4 eigen3
```

When running `cmake`:
```
export CMAKE_PREFIX_PATH=/opt/local/libexec/opencv4/cmake/
cmake -DCMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES=/opt/local/include ..
```
