Re-export HPKE for `enclave_encrypt:: EnclaveEncryptClient` users

[r-n-o]

When instantiating EnclaveEncryptClient users need to reach into HPKE because from_enclave_auth_key_and_target_key requires hpke::Kem:

rust-sdk/enclave_encrypt/src/client.rs

Lines 308 to 318 in bbd8ea7

	pub fn from_enclave_auth_key_and_target_key(
	enclave_auth_key: VerifyingKey,
	target_public_key: <Kem as KemTrait>::PublicKey,
	target_private_key: <Kem as KemTrait>::PrivateKey,
	) -> Self {
	Self {
	enclave_auth_key,
	target_public: Some(target_public_key),
	target_private: Some(target_private_key),
	}
	}