chore: address comments.

Author: blakeli0

sdk-platform-java/gax-java/gax/src/main/java/com/google/api/gax/tracing/OpenTelemetryMetricsFactory.java

@@ -42,7 +42,7 @@
 @InternalApi
 public class OpenTelemetryMetricsFactory implements ApiTracerFactory {
 
-  private ApiTracerContext clientLevelTracerContext;
+  private final ApiTracerContext clientLevelTracerContext;
   private final OpenTelemetry openTelemetry;
   private GoldenSignalsMetricsRecorder metricsRecorder;
 

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/tracing/OpenTelemetryMetricsFactoryTest.java

@@ -56,6 +56,7 @@ void newTracerWithSpanName_shouldCreateTracer_ifMetricsRecorderIsNotNull() {
         factoryWithContext.newTracer(
             mock(ApiTracer.class), mock(SpanName.class), ApiTracerFactory.OperationType.Unary);
     assertThat(actual).isInstanceOf(OpenTelemetryMetricsTracer.class);
+    assertThat(factoryWithContext).isNotEqualTo(tracerFactory);
   }
 
   @Test