[thorimur]

This PR provides basic diffing utilities for managing statistics shown by #import_diff. The two main types are

• Transition α: contains an initial : α and final : α state
• Venn α: models a Venn-diagram-like comparison between the initial and final states of a Transition α, recording a plus : α, minus : α, and shared : α.

We also include basic rendering utilities for building up tables of measurements, and basic instances for ImportGraph shake types.

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• depends on: feat: utilities for formatting tables #191