Finally make modular-frost work with alloc alone

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

crypto/frost/src/lib.rs

@@ -1,8 +1,11 @@
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![doc = include_str!("../README.md")]
+#![cfg_attr(not(feature = "std"), no_std)]
 
 use core::fmt::Debug;
-use std::collections::HashMap;
+#[allow(unused_imports)]
+use std_shims::prelude::*;
+use std_shims::collections::HashMap;
 
 use thiserror::Error;