feat: Make SerDe optional

src/metrics/cluster_hcv.rs

@@ -1,10 +1,11 @@
-use serde::{Deserialize, Serialize};
+#[cfg(feature = "serde")] use serde::{Deserialize, Serialize};
 
 use crate::linalg::BaseVector;
 use crate::math::num::RealNumber;
 use crate::metrics::cluster_helpers::*;
 
-#[derive(Serialize, Deserialize, Debug)]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+#[derive(Debug)]
 /// Homogeneity, completeness and V-Measure scores.
 pub struct HCVScore {}