Update SharedSecret byte access and deprecate old methods

Modify SharedSecret::as_secret_bytes() to return &[u8; SHARED_SECRET_SIZE]
instead of [u8; SHARED_SECRET_SIZE] to avoid unnecessary copying
of the underlying secret.

Deprecates the following methods in favor of the newly standardized
`secret_bytes` naming convention:
- `to_secret_bytes` (use `as_secret_bytes`)
- `from_bytes` (use `from_secret_bytes`)

This completes the transition to the standardized byte conversion API
while maintaining backward compatibility.

Author: Abeeujah

src/ecdh.rs

@@ -55,11 +55,12 @@ impl SharedSecret {
 
     /// Returns the shared secret as a byte value.
     #[inline]
+    #[deprecated(since = "TBD", note = "use Shared::Secret::as_secret_bytes instead")]
     pub fn to_secret_bytes(&self) -> [u8; SHARED_SECRET_SIZE] { self.0 }
 
     /// Returns the shared secret as secret bytes
     #[inline]
-    pub fn as_secret_bytes(&self) -> [u8; SHARED_SECRET_SIZE] { self.0 }
+    pub fn as_secret_bytes(&self) -> &[u8; SHARED_SECRET_SIZE] { &self.0 }
 
     /// Returns the shared secret as a byte value.
     #[deprecated(since = "TBD", note = "Use `to_secret_bytes` instead.")]
@@ -68,6 +69,7 @@ impl SharedSecret {
 
     /// Creates a shared secret from `bytes` array.
     #[inline]
+    #[deprecated(since = "TBD", note = "use SharedSecret::from_secret_bytes instead")]
     pub fn from_bytes(bytes: [u8; SHARED_SECRET_SIZE]) -> SharedSecret { SharedSecret(bytes) }
 
     /// Creates a shared secret from a secret `bytes` array.