feat: Operation and constructor declarations in `hugr-model` #2426

Job	Run time
Check for changes	7s
tests (Rust 1.75)	2m 0s
check	1m 7s
tests (Rust nightly, coverage)	1m 52s
tests (Rust beta)	2m 10s
Build benchmarks 🏋️	5m 50s
tests (Rust stable, all features)	1m 53s
tests (Rust stable, no features)	1m 13s
rs-semver-checks / Rust semver-checks 🦀	3m 13s
Check standard extensions	4s
Required checks 🦀	1s
	19m 30s

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