feat(sdk): OPAQUE auth module with state persistence

crates/quicproquo-sdk/src/events.rs

@@ -9,6 +9,15 @@ pub enum ClientEvent {
     /// Disconnected from the server.
     Disconnected { reason: String },
 
+    /// Registration succeeded.
+    Registered { username: String },
+
+    /// Login succeeded.
+    LoggedIn { username: String },
+
+    /// Logged out.
+    LoggedOut { username: String },
+
     /// Authentication succeeded.
     Authenticated { username: String },