add some randomness to wave function collapse worker

[Sheraff]

Adding randomness to wave function collapse makes the result prettier.

However it makes it harder to keep track of the choices made (choices become random instead of in-order), and this current implementation now creates a lot of small arrays.

We probably can make a more efficient implementation by keeping a single choices array of length width * height * tiles (since for each of the w×h cells, we can have up to t options)