fix: add tokio time feature, make SendState/RecvState::new public

- tokio 'time' feature needed for tokio::time::interval in retransmit timer
- SendState::new and RecvState::new must be pub for use from main.rs
- prefix unused tx param with underscore

gatunad/src/session.rs

@@ -33,7 +33,7 @@ pub struct RecvState {
 }
 
 impl SendState {
-    fn new() -> Self {
+    pub fn new() -> Self {
         SendState {
             send_seq: 0,
             acked_seq: 0,
@@ -83,7 +83,7 @@ impl SendState {
 }
 
 impl RecvState {
-    fn new() -> Self {
+    pub fn new() -> Self {
         RecvState {
             expected_seq: 0,
             deliver_seq: 0,
@@ -155,7 +155,7 @@ pub async fn handle_data(
     seq: u32,
     ack_seq: u32,
     payload: &[u8],
-    tx: &TxChan,
+    _tx: &TxChan,
 ) -> Result<bool, WriteError> {
     let handle = {
         let store = store.lock().expect("store lock poisoned");