Purpose

BatchReader results are transferred through the Arrow C Data Interface and require the returned
array, including nested child arrays, to have zero offsets.

This change fixes several paths that could return non-zero offsets:

• DataEvolutionFileReader could directly return a sliced singleton array.
• Parquet page filtering can produce columns with different chunk boundaries.
• Fully matched Parquet reads can have different chunk boundaries when large binary columns are
  split by Arrow.
• Arrow TableBatchReader aligns mismatched chunk boundaries by slicing columns, which can leave
  non-zero offsets in returned columns or nested children.

The change:

• Documents the zero-offset contract on BatchReader.
• Makes DataEvolutionFileReader concatenate a singleton array when its offset is non-zero.
• Adds ArrowUtils::NormalizeRecordBatchOffsets for recursively detecting non-zero child offsets.
• Reuses the utility in both page-filtered and fully matched Parquet read paths.
• Keeps the normal path lightweight by returning the original RecordBatch when all offsets are
  zero and only copying columns that require normalization.

Tests

Added the following unit test coverage:

• ArrowUtilsTest.TestNormalizeRecordBatchOffsets
  • top-level column with a non-zero offset
  • nested child with a non-zero offset
  • unchanged data after normalization
  • unaffected columns reuse their original ArrayData
  • already normalized batches use the no-copy fast path
• PageFilteredRowGroupReaderTest.NormalizesSlicedBatchOffsets
  • verifies multi-batch page-filtered reads through the recursive batch offset checks

API and Format

Documentation

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