Feature-gate all uses of arbitrary (#8867)

Feature gate all uses of `arbitrary` so it is not compiled during release builds.


Co-Authored-By: Mac L <mjladson@pm.me>

crypto/kzg/src/kzg_commitment.rs

@@ -114,6 +114,7 @@ impl Debug for KzgCommitment {
     }
 }
 
+#[cfg(feature = "arbitrary")]
 impl arbitrary::Arbitrary<'_> for KzgCommitment {
     fn arbitrary(u: &mut arbitrary::Unstructured<'_>) -> arbitrary::Result<Self> {
         let mut bytes = [0u8; BYTES_PER_COMMITMENT];