Differentiate no-std from alloc within tests/no-std

Fixes `no-std` builds for packages which intended to be `no-std` (without
`alloc`).

Updates a variety of MSRVs to 1.73 due to `flexible-transcript` no longer using
`std-shims` to achieve 1.66 (as `std-shims` requires `alloc`). A future
improvement would be for `std-shims` to have an `alloc` feature and only
provide MSRV shims without it.

crypto/transcript/Cargo.toml

@@ -7,7 +7,7 @@ repository = "https://github.com/serai-dex/serai/tree/develop/crypto/transcript"
 authors = ["Luke Parker <lukeparker5132@gmail.com>"]
 keywords = ["transcript"]
 edition = "2021"
-rust-version = "1.66"
+rust-version = "1.73"
 
 [package.metadata.docs.rs]
 all-features = true
@@ -17,8 +17,6 @@ rustdoc-args = ["--cfg", "docsrs"]
 workspace = true
 
 [dependencies]
-std-shims = { path = "../../common/std-shims", version = "0.1.4", default-features = false }
-
 zeroize = { version = "^1.5", default-features = false }
 
 digest = { version = "0.10", default-features = false, features = ["core-api"] }
@@ -31,7 +29,7 @@ sha2 = { version = "0.10", default-features = false }
 blake2 = { version = "0.10", default-features = false }
 
 [features]
-std = ["std-shims/std", "zeroize/std", "digest/std", "blake2?/std", "merlin?/std"]
+std = ["zeroize/std", "digest/std", "blake2?/std", "merlin?/std"]
 recommended = ["blake2"]
 tests = []
 default = ["std"]

crypto/transcript/src/lib.rs

@@ -2,9 +2,6 @@
 #![doc = include_str!("../README.md")]
 #![no_std]
 
-#[allow(unused_imports)]
-use std_shims::prelude::*;
-
 use zeroize::Zeroize;
 
 use digest::{