chore: Drop viz_hugr test utils #2463

Job	Run time
Check for changes	4s
Check Python code 🐍	2m 4s
tests (Rust stable, no features)	2m 10s
Build benchmarks 🏋️	4m 53s
Check Rust code 🦀	1m 54s
tests (Python, coverage)	2m 41s
tests (Rust nightly, coverage)	2m 42s
tests (Rust stable, all features)	1m 33s
tests (Rust 1.75)	2m 36s
tests (Rust beta)	2m 26s
Check standard extensions	1m 20s
Required checks 🦀+🐍	1s
	24m 24s

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