fix(client): validate blocking receive lifecycle before socket I/O

Blocking receives previously checked lifecycle only after a datagram arrived, allowing invalid operations to block or return empty success after timeout. Reuse session validation before socket access and cover connected, closed, and no-test-completed states through public APIs.

crates/irtt-client/src/session/machine.rs

@@ -591,7 +591,6 @@ impl SessionMachine {
         }
     }
 
-    #[cfg(feature = "tokio")]
     pub(crate) fn ensure_open(&self) -> Result<(), ClientError> {
         self.open_session().map(|_| ())
     }