🚶make the solver a generator

[cognominal]

the goal is to enumerate partial solutions to display one and go to the next so no array is kept.

and update the PPBoard accordingly. Done.

[cognominal]

it works but needs parameterizing to return intermediary results according to a chosen optional number of laid tiles.
Also need to implement the logic to refuse a tentative when empty connected component is smaller than the smaller tile.
A good way to display this connected component would be nice reusing the logic of laid tiles.

The logic to calculate connected component is already there at connexParts