feat(auth): implement OAuth2 token auto-refresh for REST catalog

Replace the MakeOAuth2 stub with a full OAuth2AuthSession that automatically refreshes tokens before expiration using the client_credentials grant.

Author: shuxu.li

src/iceberg/test/transform_util_test.cc

@@ -21,6 +21,8 @@
 
 #include <gtest/gtest.h>
 
+#include "iceberg/test/matchers.h"
+
 namespace iceberg {
 
 TEST(TransformUtilTest, HumanYear) {

src/iceberg/util/transform_util.h

@@ -24,6 +24,7 @@
 #include <string_view>
 
 #include "iceberg/iceberg_export.h"
+#include "iceberg/result.h"
 
 namespace iceberg {