Fix key error bug in iou

[cmalinmayor]

Proposed Change

Found a bug that wasn't caught by our tests because they are too small. No longer try to set IOU for non-existing edges.

Checklist

Go through these things before merge. Actions should run automatically to test them, but for information on how to run locally, see CONTRIBUTING.md.

• [x] I have added tests that prove that my feature works in various situations or tests the bugfix (if applicable).
• [x] I have checked that the tests pass and I maintained or improved test coverage (if applicable).
• [x] I have written docstrings and checked that they render correctly in the documentation build.
• [x] I have checked that mypy type checking passes.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.95%. Comparing base (7820cca) to head (2aecf79).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8 +/- ## ========================================== + Coverage 83.90% 83.95% +0.05% ========================================== Files 12 12 Lines 292 293 +1 ========================================== + Hits 245 246 +1 Misses 47 47 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.