chore: add expect_stat, expect_single_stat in GetStat trait (lancedb#3126)

This PR tries to add helper function `expect_stat` and
`expect_single_stat` to make DataBlock statistics easier to use.

Author: broccoliSpicy

rust/lance-encoding/src/data.rs

@@ -951,17 +951,17 @@ impl DataBlock {
     as_type_ref!(as_variable_width_ref, VariableWidth, VariableWidthBlock);
     as_type_ref!(as_struct_ref, Struct, StructDataBlock);
     as_type_ref!(as_dictionary_ref, Dictionary, DictionaryDataBlock);
-    as_type_ref_mut!(as_all_null_mut_ref, AllNull, AllNullDataBlock);
-    as_type_ref_mut!(as_nullable_mut_ref, Nullable, NullableDataBlock);
-    as_type_ref_mut!(as_fixed_width_mut_ref, FixedWidth, FixedWidthDataBlock);
+    as_type_ref_mut!(as_all_null_ref_mut, AllNull, AllNullDataBlock);
+    as_type_ref_mut!(as_nullable_ref_mut, Nullable, NullableDataBlock);
+    as_type_ref_mut!(as_fixed_width_ref_mut, FixedWidth, FixedWidthDataBlock);
     as_type_ref_mut!(
-        as_fixed_size_list_mut_ref,
+        as_fixed_size_list_ref_mut,
         FixedSizeList,
         FixedSizeListBlock
     );
-    as_type_ref_mut!(as_variable_width_mut_ref, VariableWidth, VariableWidthBlock);
-    as_type_ref_mut!(as_struct_mut_ref, Struct, StructDataBlock);
-    as_type_ref_mut!(as_dictionary_mut_ref, Dictionary, DictionaryDataBlock);
+    as_type_ref_mut!(as_variable_width_ref_mut, VariableWidth, VariableWidthBlock);
+    as_type_ref_mut!(as_struct_ref_mut, Struct, StructDataBlock);
+    as_type_ref_mut!(as_dictionary_ref_mut, Dictionary, DictionaryDataBlock);
 }
 
 // Methods to convert from Arrow -> DataBlock

rust/lance-encoding/src/encoder.rs

@@ -791,9 +791,7 @@ impl CompressionStrategy for CoreArrayEncodingStrategy {
         data: &DataBlock,
     ) -> Result<Box<dyn MiniBlockCompressor>> {
         if let DataBlock::FixedWidth(ref fixed_width_data) = data {
-            let bit_widths = data
-                .get_stat(Stat::BitWidth)
-                .expect("FixedWidthDataBlock should have valid `Stat::BitWidth` statistics");
+            let bit_widths = data.expect_stat(Stat::BitWidth);
             // Temporary hack to work around https://github.com/lancedb/lance/issues/3102
             // Ideally we should still be able to bit-pack here (either to 0 or 1 bit per value)
             let has_all_zeros = bit_widths
@@ -812,15 +810,9 @@ impl CompressionStrategy for CoreArrayEncodingStrategy {
         }
         if let DataBlock::VariableWidth(ref variable_width_data) = data {
             if variable_width_data.bits_per_offset == 32 {
-                let data_size = variable_width_data.get_stat(Stat::DataSize).expect(
-                    "VariableWidth DataBlock should have valid `Stat::DataSize` statistics",
-                );
-                let data_size = data_size.as_primitive::<UInt64Type>().value(0);
-
-                let max_len = variable_width_data.get_stat(Stat::MaxLength).expect(
-                    "VariableWidth DataBlock should have valid `Stat::DataSize` statistics",
-                );
-                let max_len = max_len.as_primitive::<UInt64Type>().value(0);
+                let data_size =
+                    variable_width_data.expect_single_stat::<UInt64Type>(Stat::DataSize);
+                let max_len = variable_width_data.expect_single_stat::<UInt64Type>(Stat::MaxLength);
 
                 if max_len >= FSST_LEAST_INPUT_MAX_LENGTH
                     && data_size >= FSST_LEAST_INPUT_SIZE as u64

rust/lance-encoding/src/encodings/physical/bitpack_fastlanes.rs

@@ -1573,9 +1573,7 @@ macro_rules! chunk_data_impl {
         let data_buffer = $data.data.borrow_to_typed_slice::<$data_type>();
         let data_buffer = data_buffer.as_ref();
 
-        let bit_widths = $data
-            .get_stat(Stat::BitWidth)
-            .expect("FixedWidthDataBlock should have valid bit width statistics");
+        let bit_widths = $data.expect_stat(Stat::BitWidth);
         let bit_widths_array = bit_widths
             .as_any()
             .downcast_ref::<PrimitiveArray<UInt64Type>>()