Improve Visuals of Simod-created Models

Models discovered by Simod have visual issues, such as arrows being obscured by their source and target nodes. This, e.g., hinders discerning which edges are incoming and outgoing of gateways.

Using bpmn-js features, the visuals of the models should be improvable.

Start by locating the bpmn-js integration used to render Simod-created models and inspect how node and edge visuals are configured. Compare the rendered gateways and their incoming and outgoing arrows, then confirm that the updated visuals make edge direction discernible without arrows being obscured by source or target nodes.

Written by the indexing model from the issue text.