Move elgamal encryption and `RecipientParameters` to `phoenix-core` #370

Job	Run time
Dusk Analyzer / Dusk Analyzer	8s
test cirucits / Run tests	16s
Code Analysis / Rust Format	9s
Code Analysis / Clippy Check	21s
test core / Run tests	14s
test core rkyv compiles / Run tests	14s
	1m 22s

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