Bump to arkworks-0.4.0 (#126)

* Bump to arkworks-0.4.0

* Replace remaining usages of `msm_bigint` with `msm_unchecked`

Using `msm_unchecked` instead of `msm_bigint` allows to delete the BigInt conversion code by letting the library take care of it.

transcript/src/lib.rs

@@ -126,6 +126,6 @@ impl<F: PrimeField> IOPTranscript<F> {
 macro_rules! to_bytes {
     ($x:expr) => {{
         let mut buf = ark_std::vec![];
-        ark_serialize::CanonicalSerialize::serialize($x, &mut buf).map(|_| buf)
+        ark_serialize::CanonicalSerialize::serialize_compressed($x, &mut buf).map(|_| buf)
     }};
 }