Visualize Differences in Fixture Tests

We had the start of some work towards using https://github.com/mapnik/geometry-test-data/ for fixture testing as part of Wagyu and this is excellent! However, it is very difficult to see differences in the results from wagyu currently as we can not visually inspect the differences quickly. Additionally the input and output formats are not in a format that can be easily loaded into other software. Perhaps updating this to be geojson or another format?

/cc @tcql @jakepruitt

Start by inspecting Wagyu's existing fixture-testing setup and how it uses the geometry-test-data repository. Done should include a quick way to visualize differences in fixture results and an input/output format, such as GeoJSON, that other software can load.

Written by the indexing model from the issue text.