Hypergraph foliation

[toumix]

The monoidal.Diagram.foliation method is very slow and it works only for planar diagrams.

We need a symmetric.Diagram.foliation which would use the hypergraph data structure under the hood. The output should be a list of diagrams of depth 1 (not counting swaps) which together compose back to self. The algorithm should be very simple: iterate through the boxes of the hypergraph and check if the next box is connected to the previous layer, if it isn't then add it otherwise start a new layer.

It is not entirely clear how to store this output. We could just return a list of diagrams, but what would be awesome is to return one diagram where the layers have more than one box, alternating with permutations.