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/mod.rs

@@ -1,6 +1,6 @@
 use std::collections::HashMap;
 
-use rand::{RngCore, CryptoRng};
+use rand_core::{RngCore, CryptoRng};
 
 pub use dkg::tests::{key_gen, recover_key};