Move elgamal encryption and `RecipientParameters` to `phoenix-core` #371

Job	Run time
Dusk Analyzer / Dusk Analyzer	8s
Code Analysis / Rust Format	8s
test cirucits / Run tests	3m 9s
Code Analysis / Clippy Check	15s
test core / Run tests	13s
test core rkyv compiles / Run tests	15s
	4m 8s

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