feat: Constant values in `hugr-model` #3212

Job	Run time
Check for changes	4s
check	1m 18s
tests (Rust 1.75)	2m 23s
tests (Rust nightly, coverage)	3m 10s
Build benchmarks 🏋️	2m 0s
tests (Rust beta)	2m 22s
tests (Rust stable, all features)	1m 56s
tests hugr-llvm	0s
tests (Rust stable, no features)	1m 9s
Check standard extensions	11s
Required checks 🦀	1s
	14m 34s

Provide feedback