chore: Drop viz_hugr test utils #2461

Job	Run time
Check for changes	5s
tests (Rust stable, no features)	1m 46s
Check Rust code 🦀	1m 55s
Check Python code 🐍	2m 18s
Build benchmarks 🏋️	4m 42s
tests (Rust nightly, coverage)	2m 15s
tests (Rust 1.75)	2m 47s
tests (Rust stable, all features)	2m 9s
tests (Python, coverage)	2m 14s
tests (Rust beta)	2m 40s
Check standard extensions	1m 16s
Required checks 🦀+🐍	1s
	24m 8s

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