Move elgamal encryption and `RecipientParameters` to `phoenix-core` #373

Job	Run time
Code Analysis / Clippy Check	17s
Dusk Analyzer / Dusk Analyzer	6s
Code Analysis / Rust Format	6s
test cirucits / Run tests	3m 9s
test core / Run tests	13s
test core rkyv compiles / Run tests	13s
	4m 4s

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