Finally make modular-frost work with alloc alone

Carries the update to `frost-schnorrkel` and `bitcoin-serai`.

crypto/schnorrkel/src/lib.rs

@@ -1,7 +1,10 @@
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
 
-use std::io::{self, Read};
+#[allow(unused_imports)]
+use std_shims::prelude::*;
+use std_shims::io::{self, Read};
 
 use rand_core::{RngCore, CryptoRng};
 

crypto/schnorrkel/src/tests.rs

@@ -1,6 +1,6 @@
 use rand_core::OsRng;
 
-use group::GroupEncoding;
+use ciphersuite::group::GroupEncoding;
 use frost::{
   Participant,
   tests::{key_gen, algorithm_machines, sign},