improve complexity of updating uid

[maximelucas]

From #225 (comment) by @nwlandry:

The only concern that I have with this is that it would be amazing if we could somehow leverage the self._edge_uid to make this an O(1) update instead of an O(|E|) update. As in, once we validate the edges that have been added to update self._edge_uid, we shouldn't need to iterate over these edges again when we update again.

One way to fix it would be to collect all "valid integer" new IDs when checking if they exist already.
From this we take the max, compare it to the current H._edge_uid and update it if the new value is larger. This would break the update_uid function into two separate parts.