Add `owns` and `owns_unchecked` to `SecretKey` #390

Job	Run time
test core / Run tests	12s
Dusk Analyzer / Dusk Analyzer	6s
Code Analysis / Rust Format	7s
Code Analysis / Clippy Check	12s
test core rkyv compiles / Run tests	12s
test cirucits / Run tests	3m 4s
	3m 53s

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