feat: Support `FunctionType` values #36

Job	Run time
Check for changes in Rust files	6s
Build benchmarks 🏋️	0s
tests (Rust 1.75)	44s
tests (Rust stable, all features)	50s
check	40s
tests (Rust beta)	1m 6s
tests (Rust nightly-2024-05-22)	37s
Required checks 🦀	1s
coverage	47s
	4m 51s

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