Arrow sizes in guide_edge_direction are broken

The calculation of the length of the arrows in the guide_edge_direction legends appears to have changed, and the default lengths are far too long. This can be seen in the examples at https://ggraph.data-imaginist.com/reference/guide_edge_direction.html

I took a quick look at the `edge_direction.R` file, which is where I think the problem is, but couldn't quite parse what it's doing.