Move verify_share to return batch-verifiable statements

While the previous construction achieved n/2 average detection,
this will run in log2(n). Unfortunately, the need to keep entropy
around (or take in an RNG here) remains.

crypto/frost/src/tests/vectors.rs

@@ -5,7 +5,7 @@ use std::collections::HashMap;
 use std::str::FromStr;
 
 use zeroize::Zeroizing;
-use rand::{RngCore, CryptoRng};
+use rand_core::{RngCore, CryptoRng};
 
 use group::{ff::PrimeField, GroupEncoding};