crypto-common: rename serializable_state module to hazmat (#1487)

Also removes the toplevel re-exports for the traits, forcing users to go
through the now `pub hazmat` module.

There's a lot of misuse potential with these traits, which are intended
to make it possible to serialize/deserialize the internal state of hash
functions. However previously they were presented side-by-side with
other traits, which made that unclear.

This commit deliberately doesn't make other changes to the file so git
will preserve its history:

    diff --git a/crypto-common/src/serializable_state.rs b/crypto-common/src/hazmat.rs
    similarity index 100%
    rename from crypto-common/src/serializable_state.rs
    rename to crypto-common/src/hazmat.rs

It would be very good for a followup commit to massively expand the
documentation around both the module and the traits, especially to spell
out the various ways they can be misused.

Cargo.toml

@@ -16,4 +16,6 @@ members = [
 ]
 
 [patch.crates-io]
+crypto-common = { path = "./crypto-common" }
+digest = { path = "./digest" }
 signature = { path = "./signature" }

crypto-common/src/lib.rs

@@ -12,6 +12,9 @@
 #[cfg(feature = "std")]
 extern crate std;
 
+/// Hazardous materials.
+pub mod hazmat;
+
 #[cfg(feature = "getrandom")]
 pub use getrandom;
 #[cfg(feature = "rand_core")]
@@ -29,12 +32,6 @@ use hybrid_array::{
 #[cfg(feature = "rand_core")]
 use rand_core::CryptoRngCore;
 
-mod serializable_state;
-pub use serializable_state::{
-    AddSerializedStateSize, DeserializeStateError, SerializableState, SerializedState,
-    SubSerializedStateSize,
-};
-
 /// Block on which [`BlockSizeUser`] implementors operate.
 pub type Block<B> = Array<u8, <B as BlockSizeUser>::BlockSize>;
 

digest/src/core_api/ct_variable.rs

@@ -14,9 +14,9 @@ use core::{
 };
 use crypto_common::{
     array::{Array, ArraySize},
+    hazmat::{DeserializeStateError, SerializableState, SerializedState, SubSerializedStateSize},
     typenum::{IsLess, IsLessOrEqual, Le, LeEq, NonZero, Sum, U1, U256},
-    Block, BlockSizeUser, DeserializeStateError, OutputSizeUser, SerializableState,
-    SerializedState, SubSerializedStateSize,
+    Block, BlockSizeUser, OutputSizeUser,
 };
 
 /// Dummy type used with [`CtVariableCoreWrapper`] in cases when

digest/src/core_api/rt_variable.rs

@@ -9,11 +9,11 @@ use core::{
     fmt,
     ops::{Add, Sub},
 };
-use crypto_common::SubSerializedStateSize;
 use crypto_common::{
     array::{Array, ArraySize},
+    hazmat::{DeserializeStateError, SerializableState, SerializedState, SubSerializedStateSize},
     typenum::{Diff, IsLess, Le, NonZero, Sum, Unsigned, U1, U256},
-    AddBlockSize, DeserializeStateError, SerializableState, SerializedState, SubBlockSize,
+    AddBlockSize, SubBlockSize,
 };
 #[cfg(feature = "zeroize")]
 use zeroize::ZeroizeOnDrop;

digest/src/core_api/wrapper.rs

@@ -13,9 +13,9 @@ use core::{
 };
 use crypto_common::{
     array::{Array, ArraySize},
+    hazmat::{DeserializeStateError, SerializableState, SerializedState, SubSerializedStateSize},
     typenum::{Diff, IsLess, Le, NonZero, Sum, U1, U256},
-    BlockSizeUser, DeserializeStateError, InvalidLength, Key, KeyInit, KeySizeUser, Output,
-    SerializableState, SerializedState, SubSerializedStateSize,
+    BlockSizeUser, InvalidLength, Key, KeyInit, KeySizeUser, Output,
 };
 
 #[cfg(feature = "mac")]