refactor(metrics): warn with the remaining count and document NaN pairs (SIENTIAPDE-2215)

tests/utils/repository/test_data_manager_repository.py

@@ -323,10 +323,14 @@ def test_compute_regression_metrics_ignores_nan_pairs():
 
     wrapper = MagicMock()
     wrapper.model = object()  # no sklearn .regr -> equation extraction is skipped
-    out = repo.compute_regression_metrics(tmr, wrapper)
+    with patch.object(repo, 'warning') as warn:
+        out = repo.compute_regression_metrics(tmr, wrapper)
 
     assert out.mse_val == 0.0
     assert out.mae_val == 0.0
+    assert out.r2_val == 1.0
+    warn.assert_called_once()
+    assert 'Ignoring 2 of 4' in warn.call_args.args[0]
 
 
 def test_compute_regression_metrics_all_nan_pairs_raises():