more ergonomic lax::OpenHypergraph::new_edge

[statusfailed]

... which now accepts any pair of types which can be converted to a Vec<NodeId>, and then packs those in a Hyperedge.

This makes it a lot more ergonomic; see e.g.:

state.new_edge(Arr::Eq, ([i, j], [e]));

vs

state.new_edge(Arr::Eq, Hyperedge { sources: vec![i, j], targets: vec![e] });