Remove `KeyOwned` (#498) #319

Job	Run time
test mdBook	53s
cargo test on ubuntu, rust stable	53s
cargo test on ubuntu, rust 1.78	1m 2s
cargo test on macos, rust stable	1m 8s
cargo test on macos, rust 1.78	1m 21s
cargo test on windows, rust stable	2m 14s
cargo test on windows, rust 1.78	1m 35s
	9m 6s

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