refactor(identity): follow naming conventions for conversion methods

This PR renames some method names that don't follow Rust naming conventions or behave differently from what the name suggests:
- Enforce "try" prefix on all methods that return `Result`.
- Enforce "encode" method name for methods that return encoded bytes.
- Enforce "to_bytes" method name for methods that return raw bytes.
- Enforce "decode" method name for methods that convert encoded key.
- Enforce "from_bytes" method name for methods that convert raw bytes.

Pull-Request: #3775.

core/src/signed_envelope.rs

@@ -76,7 +76,7 @@ impl SignedEnvelope {
         use quick_protobuf::MessageWrite;
 
         let envelope = proto::Envelope {
-            public_key: self.key.to_protobuf_encoding(),
+            public_key: self.key.encode_protobuf(),
             payload_type: self.payload_type,
             payload: self.payload,
             signature: self.signature,
@@ -101,7 +101,7 @@ impl SignedEnvelope {
             proto::Envelope::from_reader(&mut reader, bytes).map_err(DecodeError::from)?;
 
         Ok(Self {
-            key: PublicKey::from_protobuf_encoding(&envelope.public_key)?,
+            key: PublicKey::try_decode_protobuf(&envelope.public_key)?,
             payload_type: envelope.payload_type.to_vec(),
             payload: envelope.payload.to_vec(),
             signature: envelope.signature.to_vec(),