feat(identity): make Keypair and Publickey opaque

`Keypair` and `Publickey` are rendered opaque:
- `Keypair` is replaced by a private `KeyPairInner` enum that is encapsulated inside the `Keypair` `pub struct`
- `Publickey` is replaced by a private `PublickeyInner` enum that is encapsulated inside the `Publickey` `pub struct`

Resolves #3860.

Pull-Request: #3866.

identity/CHANGELOG.md

@@ -5,8 +5,12 @@
 - Add support for exporting and importing ECDSA keys via the libp2p [protobuf format].
   See [PR 3863].
 
+- Make `Keypair` and `PublicKey` opaque.
+  See [PR 3866].
+
 [PR 3715]: https://github.com/libp2p/rust-libp2p/pull/3715
 [PR 3863]: https://github.com/libp2p/rust-libp2p/pull/3863
+[PR 3866]: https://github.com/libp2p/rust-libp2p/pull/3866
 [protobuf format]: https://github.com/libp2p/specs/blob/master/peer-ids/peer-ids.md#keys
 
 ## 0.1.2

identity/Cargo.toml

@@ -20,7 +20,7 @@ log = "0.4"
 multiaddr = { version = "0.17.1", optional = true }
 multihash = { version = "0.17.0", default-features = false, features = ["std"], optional = true }
 p256 = { version = "0.13", default-features = false, features = ["ecdsa", "std", "pem"], optional = true }
-quick-protobuf = { version = "0.8.1", optional = true }
+quick-protobuf = "0.8.1"
 rand = { version = "0.8", optional = true }
 sec1 = { version = "0.7", default-features = false, optional = true }
 serde = { version = "1", optional = true, features = ["derive"] }
@@ -33,10 +33,10 @@ zeroize = { version = "1.6", optional = true }
 ring = { version = "0.16.9", features = ["alloc", "std"], default-features = false, optional = true}
 
 [features]
-secp256k1 = [ "dep:libsecp256k1", "dep:asn1_der", "dep:rand", "dep:sha2", "dep:zeroize", "dep:quick-protobuf" ]
-ecdsa = [ "dep:p256", "dep:rand", "dep:void", "dep:zeroize", "dep:sec1", "dep:quick-protobuf" ]
-rsa = [ "dep:ring", "dep:asn1_der", "dep:rand", "dep:zeroize", "dep:quick-protobuf" ]
-ed25519 = [ "dep:ed25519-dalek", "dep:rand", "dep:zeroize", "dep:quick-protobuf" ]
+secp256k1 = [ "dep:libsecp256k1", "dep:asn1_der", "dep:rand", "dep:sha2", "dep:zeroize" ]
+ecdsa = [ "dep:p256", "dep:rand", "dep:void", "dep:zeroize", "dep:sec1" ]
+rsa = [ "dep:ring", "dep:asn1_der", "dep:rand", "dep:zeroize" ]
+ed25519 = [ "dep:ed25519-dalek", "dep:rand", "dep:zeroize" ]
 peerid = [ "dep:multihash", "dep:multiaddr", "dep:bs58", "dep:rand", "dep:thiserror", "dep:sha2" ]
 
 [dev-dependencies]

identity/src/error.rs

@@ -33,6 +33,7 @@ pub struct DecodingError {
 }
 
 impl DecodingError {
+    #[allow(dead_code)]
     pub(crate) fn missing_feature(feature_name: &'static str) -> Self {
         Self {
             msg: format!("cargo feature `{feature_name}` is not enabled"),