test: Reorg OutlineCfg/nest_cfgs tests so hugr doesn't depend on algorithm #367

Job	Run time
Check for changes in Rust files	3s
benches	1m 36s
tests (Rust stable)	1m 43s
tests (Rust 1.75)	1m 35s
check	1m 2s
tests (Rust beta)	1m 19s
tests (Rust nightly)	1m 13s
Required checks 🦀	1s
coverage	1m 48s
	10m 20s

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