chore: Drop viz_hugr test utils #2460

Job	Run time
Check for changes	6s
Check Python code 🐍	2m 29s
Build benchmarks 🏋️	5m 0s
Check Rust code 🦀	2m 9s
tests (Rust 1.75)	2m 48s
tests (Rust stable, no features)	2m 2s
tests (Rust beta)	2m 49s
tests (Rust nightly, coverage)	2m 38s
tests (Python, coverage)	2m 39s
tests (Rust stable, all features)	2m 6s
Check standard extensions	1m 17s
Required checks 🦀+🐍	1s
	26m 4s

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