refactor(client): separate probe scheduling from session state

crates/irtt-client/src/client/tests/close.rs

@@ -118,6 +118,7 @@ fn close_flagged_echo_reply_emits_reply_then_closes_without_sending_close() {
     ));
     assert_eq!(events.len(), 2);
     assert!(client.next_send_deadline().is_none());
+    assert!(client.schedule.is_none());
     assert!(matches!(
         client.send_probe(),
         Err(ClientError::AlreadyClosed)

crates/irtt-client/src/client/tests/no_test.rs

@@ -8,8 +8,11 @@ fn no_test_success_validates_params() {
     let server = no_test_server(params.clone(), 0);
     config.server_addr = server.addr.to_string();
     let mut client = Client::connect(config).unwrap();
+    assert!(client.next_send_deadline().is_none());
     let negotiated = assert_no_test_completed(client.open().unwrap());
     assert_eq!(negotiated.params, params);
+    assert!(client.next_send_deadline().is_none());
+    assert!(client.schedule.is_none());
     server.join();
 }
 

crates/irtt-client/src/client/tests/probes_replies/probe_schedule.rs

@@ -20,6 +20,7 @@ fn send_probe_sends_valid_echo_request() {
         ..default_test_config(server.addr)
     };
     let mut client = Client::connect(config).unwrap();
+    assert!(client.next_send_deadline().is_none());
     assert_open_started(client.open().unwrap());
     let events = client.send_probe().unwrap();
     assert_eq!(events.len(), 1);