Non-optional dependency marked as optional

[souragc]

curve25519-dalek is a required dependency but is marked as optional in the manifest file. No attributes are gating the path to its usage.

Cargo.toml

curve25519-dalek = { version = "4", optional = true }

The use chain is:
lib.rs -> ecvrf/mod.rs -> ecvrf/ecvrf_impl.rs

lib.rs

pub mod ecvrf;

ecvrf/mod.rs

mod ecvrf_impl;

ecvrf/ecvrf_impl.rs

use curve25519_dalek::digest::Update;
use curve25519_dalek::traits::IsIdentity;
use curve25519_dalek::{
    constants::ED25519_BASEPOINT_POINT,
    edwards::{CompressedEdwardsY, EdwardsPoint},
    scalar::Scalar as ed25519_Scalar,
};