fix: Return raw bytes for Unknown message payload encoding

Fix consensus_encode_payload for Unknown message variants to return
the raw payload bytes directly instead of using serialize() which
adds a VarInt length prefix. This matches consensus_decode_payload
which expects raw bytes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: PastaPastaPasta

dash/src/network/message.rs

@@ -408,7 +408,7 @@ impl NetworkMessage {
             NetworkMessage::Unknown {
                 payload: ref data,
                 ..
-            } => serialize(data),
+            } => data.clone(),
             NetworkMessage::Verack
             | NetworkMessage::SendHeaders
             | NetworkMessage::SendHeaders2