Add fast slab lookup for the GeometryOracle, replacing knn as the default

miniCaloSim's detector is a stack of planar layer slabs along one axis, so
material/layer_id are a pure function of depth. The new "slab" method
exploits this with an exact O(log #segments) binary search over
depth-axis segment boundaries, instead of a nearest-neighbour search over
hundreds of thousands of reference points — much cheaper per call, which
matters since the oracle is queried on every autoregressive rollout step.
"knn"/"svm" remain as fallbacks for non-slab geometries.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/geometry_oracle.py

@@ -16,11 +16,13 @@ from giant.geometry import build_geometry_oracle
 def run_build_geometry_oracle(
     data: Path,
     out: Path,
-    method: str = "knn",
+    method: str = "slab",
     k: int = 1,
     subsample: int = 500_000,
     escape_factor: float = 5.0,
     seed: int = 0,
+    depth_axis: int = 2,
+    n_bins: int = 2000,
 ) -> None:
     files = find_parquet_files(data)
     print(f"found {len(files)} parquet file(s); sampling up to {subsample:,} points")
@@ -32,17 +34,33 @@ def run_build_geometry_oracle(
         subsample=subsample,
         escape_factor=escape_factor,
         seed=seed,
+        depth_axis=depth_axis,
+        n_bins=n_bins,
     )
 
-    print(f"method: {method}  reference points: {oracle.metadata['n_reference_points']:,}")
+    print(
+        f"method: {method}  reference points: {oracle.metadata['n_reference_points']:,}"
+    )
     print("classes (material, layer_id):")
     for material, layer_id in oracle.classes:
         print(f"  {material:<12} layer_id={layer_id}")
-    print(
-        f"median NN spacing: {oracle.metadata['median_nn_dist']:.3f}  "
-        f"escape_threshold: {oracle.escape_threshold:.3f} "
-        f"(= {escape_factor}x spacing)"
-    )
+
+    if method == "slab":
+        z_lo, z_hi = oracle.metadata["z_range"]
+        print(
+            f"depth axis: {'xyz'[depth_axis]}  segments: {oracle.metadata['n_segments']}  "
+            f"z range: [{z_lo:.3f}, {z_hi:.3f}]  radius_max: {oracle.metadata['radius_max']:.3f}"
+        )
+        print(
+            f"median depth spacing: {oracle.metadata['median_z_spacing']:.3f}  "
+            f"escape_threshold: {oracle.escape_threshold:.3f} (= {escape_factor}x spacing)"
+        )
+    else:
+        print(
+            f"median NN spacing: {oracle.metadata['median_nn_dist']:.3f}  "
+            f"escape_threshold: {oracle.escape_threshold:.3f} "
+            f"(= {escape_factor}x spacing)"
+        )
     if oracle.escape_threshold <= 0.0:
         print(
             "warning: escape_threshold is 0 (reference points are coincident) — "