feat!: Flatten `LeafOp` #118

Job	Run time
Check for changes in Rust files	5s
benches	1m 47s
tests (Rust stable)	1m 18s
tests (Rust 1.75)	1m 21s
check	50s
tests (Rust beta)	1m 16s
tests (Rust nightly)	1m 19s
Required checks 🦀	1s
coverage	1m 47s
	9m 44s

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