Enhance training analysis page with test metrics and confusion matrix

- Added a section to display test metrics for model performance on the held-out test set.
- Implemented confusion matrix visualization to analyze prediction breakdown.
- Refactored sidebar settings to streamline metric selection and improve user experience.
- Updated cross-validation statistics to compare CV performance with test metrics.
- Enhanced DatasetEnsemble methods to handle empty data scenarios gracefully.
- Introduced debug scripts to assist in identifying feature mismatches and validating dataset preparation.
- Added comprehensive tests for DatasetEnsemble to ensure feature consistency and correct behavior across various scenarios.

tests/debug_arcticdem_batch.py

@@ -0,0 +1,33 @@
+"""Debug script to check what _prep_arcticdem returns for a batch."""
+
+from entropice.ml.dataset import DatasetEnsemble
+
+ensemble = DatasetEnsemble(
+    grid="healpix",
+    level=10,
+    target="darts_mllabels",
+    members=["ArcticDEM"],
+    add_lonlat=True,
+    filter_target=False,
+)
+
+# Get targets
+targets = ensemble._read_target()
+print(f"Total targets: {len(targets)}")
+
+# Get first batch of targets
+batch_targets = targets.iloc[:100]
+print(f"\nBatch targets: {len(batch_targets)}")
+print(f"Cell IDs in batch: {batch_targets['cell_id'].values[:5]}")
+
+# Try to prep ArcticDEM for this batch
+print("\n" + "=" * 80)
+print("Calling _prep_arcticdem...")
+print("=" * 80)
+arcticdem_df = ensemble._prep_arcticdem(batch_targets)
+print(f"\nArcticDEM DataFrame shape: {arcticdem_df.shape}")
+print(f"ArcticDEM DataFrame index: {arcticdem_df.index[:5].tolist() if len(arcticdem_df) > 0 else 'EMPTY'}")
+print(
+    f"ArcticDEM DataFrame columns ({len(arcticdem_df.columns)}): {arcticdem_df.columns[:10].tolist() if len(arcticdem_df.columns) > 0 else 'NO COLUMNS'}"
+)
+print(f"Number of non-NaN rows: {arcticdem_df.notna().any(axis=1).sum()}")