chore(util): address retry review comments

Author: wgtmac

src/iceberg/test/retry_util_test.cc

@@ -210,7 +210,7 @@ TEST(RetryRunnerTest, OnlyRetryOnTakesPrecedenceOverStopRetryOn) {
                                         .max_wait_ms = 10,
                                         .total_timeout_ms = 5000})
                     .OnlyRetryOn(ErrorKind::kCommitFailed)
-                    .StopRetryOn({ErrorKind::kCommitFailed})
+                    .StopRetryOn(ErrorKind::kCommitFailed)
                     .Run(
                         [&]() -> Result<int> {
                           ++call_count;

src/iceberg/util/retry_util.h

@@ -163,15 +163,19 @@ class ICEBERG_EXPORT RetryRunner {
 
  private:
   enum class RetryPolicyMode {
+    // No retry policy was selected; invalid when retries are enabled.
     kUnset,
+    // Retry only errors listed in retry_error_kinds_.
     kOnlyRetryOn,
+    // Retry all errors except those listed in retry_error_kinds_.
     kStopRetryOn,
   };
 
   using Clock = std::chrono::steady_clock;
   using Duration = std::chrono::milliseconds;
   using TimePoint = Clock::time_point;
 
+  /// \brief Validate retry counts, timing bounds, and the selected retry policy.
   Status ValidateConfig() const;
   std::optional<TimePoint> ComputeDeadline() const;
   bool HasTimedOut(const std::optional<TimePoint>& deadline) const;