test: update hash-split expectations for DataFusion 54 foldhash

DataFusion 54's `create_hashes` uses foldhash instead of ahash, so the
concrete hash values (and therefore split assignments) differ from the
DF53 baseline:

- `test_hash_split` (Rust): recompute the expected per-split counts.
- `test_split_hash_with_discard` (Python): hash a high-cardinality
  column instead of the 2-value `category`, so the discard ratio no
  longer hinges on where two specific hashes land.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python/python/tests/test_permutation.py

@@ -134,8 +134,11 @@ def test_split_hash_with_discard(mem_db):
     )
 
     permutation_tbl = (
+        # Hash a high-cardinality column: "category" has only two distinct
+        # values, so whether anything is discarded would hinge on where those
+        # two hashes land rather than on the discard weight.
         permutation_builder(tbl)
-        .split_hash(["category"], [1, 1], discard_weight=2)  # Should discard ~50%
+        .split_hash(["id"], [1, 1], discard_weight=2)  # Should discard ~50%
         .execute()
     )
 

rust/lancedb/src/dataloader/permutation/split.rs

@@ -796,15 +796,15 @@ mod tests {
         // These assertions are all based on fixed seed in data generation but they match
         // up roughly to what we expect (25% discarded, 25% in split 0, 50% in split 1)
 
-        // 14 rows (28%) are discarded because discard_weight is 1
-        assert_eq!(split_batch.num_rows(), 36);
+        // 8 rows (16%) are discarded because discard_weight is 1
+        assert_eq!(split_batch.num_rows(), 42);
         assert_eq!(split_batch.num_columns(), 2);
 
         let split_ids = split_batch.column(1).as_primitive::<UInt64Type>().values();
         let num_in_split_0 = split_ids.iter().filter(|v| **v == 0).count();
         let num_in_split_1 = split_ids.iter().filter(|v| **v == 1).count();
 
-        assert_eq!(num_in_split_0, 11); // 22%
-        assert_eq!(num_in_split_1, 25); // 50%
+        assert_eq!(num_in_split_0, 12); // 24%
+        assert_eq!(num_in_split_1, 30); // 60%
     }
 }