feat: Operation and constructor declarations in `hugr-model` (#1605) #2435

Job	Run time
Check for changes	4s
tests (Rust nightly, coverage)	2m 43s
check	1m 10s
Build benchmarks 🏋️	5m 40s
tests (Rust stable, all features)	1m 56s
tests (Rust 1.75)	1m 54s
tests (Rust stable, no features)	1m 17s
tests (Rust beta)	1m 49s
rs-semver-checks	0s
Check standard extensions	8s
Required checks 🦀	1s
	16m 42s

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