Merge same display objects

[ships]

Description

• also, refactor some test stuff
• improve type handling
• rename methods
• generate nodeIds nondeterministically

Related Issues

Resolves #171

Checklist

• [x] I have tested these changes locally and they work as expected.
• [x] I have added or updated tests to cover any new functionality or bug fixes.
• [ ] I have updated the documentation to reflect any changes or additions to the project.
• [x] I have followed the project's code of conduct and conventions for commit messages.

Additional Information

Provide any additional information that might be helpful in understanding this pull request, such as screenshots, links to relevant research, or other context.