feat(auth): add StateStore trait for pluggable OAuth state storage (#614)

* feat(auth): add StateStore trait for pluggable OAuth state storage

* fix(examples): use CLI server_url for transport connection

examples/clients/src/auth/oauth_client.rs

@@ -173,7 +173,7 @@ async fn main() -> Result<()> {
     let client = AuthClient::new(reqwest::Client::default(), am);
     let transport = StreamableHttpClientTransport::with_client(
         client,
-        StreamableHttpClientTransportConfig::with_uri(MCP_SERVER_URL),
+        StreamableHttpClientTransportConfig::with_uri(server_url.as_str()),
     );
 
     // Create client and connect to MCP server