test: add skeleton tests/test_metrics_models.py

Author: DiogoRibeiro7

tests/test_metrics_models.py

@@ -0,0 +1,9 @@
+import importlib
+
+
+def test_import_metrics_models():
+    mod = importlib.import_module("llm_observability_analytics.metrics.models")
+    assert mod is not None
+
+
+# TODO: add numeric helper tests with small sample inputs