tests: Add near-miss power-of-2 shape (33,33,33) to benchmarks

Documents the performance penalty when a shard shape is just above a
power-of-2 boundary, causing n_z to jump from 32,768 to 262,144.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mkitti

tests/benchmarks/test_indexing.py

@@ -108,6 +108,7 @@ def read_with_cache_clear() -> None:
 large_morton_shards = (
     (32,) * 3,  # With 1x1x1 chunks: 32x32x32 = 32768 chunks per shard (power-of-2)
     (30,) * 3,  # With 1x1x1 chunks: 30x30x30 = 27000 chunks per shard (non-power-of-2)
+    (33,) * 3,  # With 1x1x1 chunks: 33x33x33 = 35937 chunks per shard (near-miss: just above power-of-2)
 )
 
 
@@ -204,6 +205,7 @@ def read_with_cache_clear() -> None:
     (20, 20, 20), # 8000 elements   (non-power-of-2)
     (32, 32, 32), # 32768 elements  (power-of-2)
     (30, 30, 30), # 27000 elements  (non-power-of-2)
+    (33, 33, 33), # 35937 elements  (near-miss: just above power-of-2, n_z=262144)
 )