feat: Experimental support for encryption using libcrux

Libcrux is a library for formally verified implementations of
cryptographic primitives. It uses multiple back ends; one of which is
libjade. A cryptographic library written in the jasmin assembly
language for high assurance cryptographic implementations.

To use compile with the experiment_libcrux feature enabled:

    cargo build --features experiment_libcrux

ciphers/src/lib.rs

@@ -9,6 +9,9 @@ const_assert!(KEY_LEN == hash_domain::KEY_LEN);
 
 /// Authenticated encryption with associated data
 pub mod aead {
+    #[cfg(not(feature = "libcrux"))]
+    pub use crate::subtle::chacha20poly1305_ietf::{decrypt, encrypt, KEY_LEN, NONCE_LEN, TAG_LEN};
+    #[cfg(feature = "libcrux")]
     pub use crate::subtle::chacha20poly1305_ietf::{decrypt, encrypt, KEY_LEN, NONCE_LEN, TAG_LEN};
 }