[red-knot] don't land, just playing around with oxidd

[carljm]

Run this using cargo run --bin red_knot; this PR replaces the entire red-knot CLI with outputting a graph visualization file instead, because it was the laziest possible way I could do this :)

To create a png file from the tdd.dot file this outputs, I used dot -Tpng tdd.dot -o tdd.png, using dot CLI from the GraphViz package.

[github-actions]

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