rfqmsg: extend IncomingMsg interface with methods MsgPeer and MsgID

This modification simplifies incoming message handling in future
commits.

rfqmsg/buy_request.go

@@ -168,6 +168,16 @@ func (q *BuyRequest) ToWire() (WireMessage, error) {
 	}, nil
 }
 
+// MsgPeer returns the peer that sent the message.
+func (q *BuyRequest) MsgPeer() route.Vertex {
+	return q.Peer
+}
+
+// MsgID returns the quote request session ID.
+func (q *BuyRequest) MsgID() ID {
+	return q.ID
+}
+
 // String returns a human-readable string representation of the message.
 func (q *BuyRequest) String() string {
 	var groupKeyBytes []byte

rfqmsg/messages.go

@@ -156,6 +156,12 @@ func WireMsgDataVersionDecoder(r io.Reader, val any, buf *[8]byte,
 // IncomingMsg is an interface that represents an inbound wire message
 // that has been received from a peer.
 type IncomingMsg interface {
+	// MsgPeer returns the peer that sent the message.
+	MsgPeer() route.Vertex
+
+	// MsgID returns the quote request session ID.
+	MsgID() ID
+
 	// String returns a human-readable string representation of the message.
 	String() string
 }

rfqmsg/reject.go

@@ -243,6 +243,16 @@ func (q *Reject) ToWire() (WireMessage, error) {
 	}, nil
 }
 
+// MsgPeer returns the peer that sent the message.
+func (q *Reject) MsgPeer() route.Vertex {
+	return q.Peer
+}
+
+// MsgID returns the quote request session ID.
+func (q *Reject) MsgID() ID {
+	return q.ID
+}
+
 // String returns a human-readable string representation of the message.
 func (q *Reject) String() string {
 	return fmt.Sprintf("Reject(id=%x, err_code=%d, err_msg=%s)",

rfqmsg/sell_request.go

@@ -174,6 +174,16 @@ func (q *SellRequest) ToWire() (WireMessage, error) {
 	}, nil
 }
 
+// MsgPeer returns the peer that sent the message.
+func (q *SellRequest) MsgPeer() route.Vertex {
+	return q.Peer
+}
+
+// MsgID returns the quote request session ID.
+func (q *SellRequest) MsgID() ID {
+	return q.ID
+}
+
 // String returns a human-readable string representation of the message.
 func (q *SellRequest) String() string {
 	var groupKeyBytes []byte