[feature] Verify that a set of attributes are equal between all wires connected to the same pin

[kvid]

Maybe a general feature to warn about differences between wires that are connected together could be useful? It must of course be possible to turn this off where differences are intended.

Originally posted by @kvid in #270 (comment)

I suggest each connector can have an attribute specifying a set of all wire attributes that should be equal when connected to the same pin (or a list of one such set per pin), e.g. like wires_equal, and then print a warning (or rise an exception) about wires that violates this.

[martinrieder]

Another use case of this would be making wire colors match. If an attribute is unspecified or explicitly set to null, the missing attributes should be made to match its connected wires.