refactor(hugr-llvm)!: Optimise the llvm types used to represent hugr sums. #3307

Job	Run time
Check for changes	5s
Build benchmarks 🏋️	3m 9s
tests (Rust nightly, coverage)	3m 20s
tests (Rust 1.75)	3m 13s
check	4m 21s
tests (Rust beta)	3m 15s
tests (Rust stable, all features)	3m 51s
tests (Rust stable, no features)	4m 9s
Check standard extensions	0s
Required checks 🦀	1s
	25m 24s

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