9eb8cc2de8
Breaking wire protocol change: MessageType field increased from 2 bytes to 4 bytes in LP packets. This future-proofs the message type space and aligns with other u32 fields. Changes: - message.rs: #[repr(u32)], from_u32(), to_u32() - error.rs: InvalidMessageType(u32) - codec.rs: All serialization/deserialization updated to 4-byte msg_type - Cleartext parsing: inner_bytes[4..8], content at [8..] - AEAD parsing: decrypted[4..8], content at [8..] - Serialization: 4 bytes for message type