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/Cargo.toml

@@ -15,8 +15,8 @@ rustdoc-args = ["--cfg", "docsrs"]
 [dependencies]
 thiserror = "1"
 
+rand_core = "0.6"
 rand_chacha = "0.3"
-rand = "0.8"
 
 zeroize = { version = "1.5", features = ["zeroize_derive"] }
 subtle = "2"