fix: make PlanarEmbedding.copy() use add_edges_from() from parent (closes #7223)

[mdealencar]

closes #7223

PlanarEmbedding inherits the method copy() from nx.Graph. However, the current implementation uses the method add_edges_from() which was made forbidden by PR #6798.

Current Behavior

embedding = nx.PlanarEmbedding({1: {2: {"cw": 2, "ccw": 2}},
                                2: {1: {"cw": 1, "ccw": 1}}})
emb2 = embedding.copy()

NotImplementedError: Use `add_half_edge` method to add edges to a PlanarEmbedding.

[rossbar]

To me, the real question is: do we want to support copying of PlanarEmbedding objects? I can't see any reason why not, so I don't object to making the copy method work.

It'd be nice to have a couple tests if for no other reason than to catch regressions, but it's not a blocker since this is technically just re-enabling behavior that was already "working" prior to #6798 !

Thanks @mdealencar !