In this repo I want you to implement a templated Wave Function Collapse engine that would be compatible with 2D grids, 3D grids, Sudoku, Picross, etc.
I want the following to be possible:

WFC::Builder<World>()
    .variable(name/id/userdata, ...).constrains([](World& world, int worldID, Constrainer& constrainer, name/id/userdata){ constrainer.constrain(world.getid(...)); })
    .variable(...)

The World is responsible for giving its size and giving ids. the ids should all fit in the size of the world.
when setting the variable on a node/cell, it should call the lambda to constrain the rest of the unknown nodes/cells.
The WFC should have no concept of coordinate systems. The WFC algorithm should be able to work even without coordinates, and just with a graph for example.

sudoku eg:
WFC::Builder<Array2D<uint8_t,9,9>>()
    .variable(1,2,3,4,5,6,7,8,9).constrains([](Array2D<uint8_t,9,9>& world, int worldID, Constrainer& constrainer, uint8_t var)
    {
        int [x,y] = world.getCoord(worldID);

        for (int i{}; i < 9; ++i)
        {
            constrainer.constrain(9 * y + i, var);
            constrainer.constrain(i * y + x, var);
            // TODO add small square constraint
        }
    })

2D tilemap eg:
WFC::Builder<Array2D<uint8_t, 100,100>>()
    .variable(SEA).constrains([](Array2D<uint8_t, 100,100>& world, int worldID, Constrainer& constrainer, uint8_t var)
    {
        int [x,y] = world.getCoord(worldID);
        
        constrainer.only(y*100 + x - 1, SEA, BEACH);
        constrainer.only(y*99 + x, SEA, BEACH);
        constrainer.only(x*101 + x, SEA, BEACH);
        constrainer.only(x*100 + x + 1, SEA, BEACH);
    })
    .variable(BEACH).constrains([](Array2D<uint8_t, 100,100>& world, int worldID, Constrainer& constrainer, uint8_t var)
    {
        int [x,y] = world.getCoord(worldID);
        
        constrainer.only(y*100 + x - 1, SEA, LAND);
        constrainer.only(y*99 + x, SEA, LAND);
        constrainer.only(x*101 + x, SEA, LAND);
        constrainer.only(x*100 + x + 1, SEA, LAND);
    })
    ...