Implement Readable for Responder

A future InvoiceReceived event will include a Responder. Since Event
implements Readable, so must Responder.

Author: jkczyz

lightning/src/onion_message/messenger.rs

@@ -325,12 +325,18 @@ impl OnionMessageRecipient {
 
 /// The `Responder` struct creates an appropriate [`ResponseInstruction`]
 /// for responding to a message.
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Responder {
 	/// The path along which a response can be sent.
 	reply_path: BlindedPath,
 	path_id: Option<[u8; 32]>
 }
 
+impl_writeable_tlv_based!(Responder, {
+	(0, reply_path, required),
+	(2, path_id, option),
+});
+
 impl Responder {
 	/// Creates a new [`Responder`] instance with the provided reply path.
 	pub(super) fn new(reply_path: BlindedPath, path_id: Option<[u8; 32]>) -> Self {