metrics tests

- Add _create_metric_stub_from_protobuf method to correctly parse protobuf metrics
- Add _extract_attributes_from_data_point helper method
- Change metric handling to use protobuf-specific parsing instead of OpenTelemetry native parsing
- Add missing typing import
- Add OTEL_METRIC_EXPORT_INTERVAL environment variable for test configuration

This fixes the CI failure where metrics were not being properly extracted from
protobuf data in server mode tests.

tests/integration/common/recordings/models-64a2277c90f0f42576f60c1030e3a020403d34a95f56931b792d5939f4cebc57-826d44c3.json

@@ -84,5 +84,6 @@
       }
     ],
     "is_streaming": false
-  }
+  },
+  "id_normalization_mapping": {}
 }