Binary search optimization for Parquet Variant's object field ID lookup

[abigalekim]

locate_object_field maps an integer dictionary ID to the encoded bytes of a field value within a Parquet Variant object blob. This function previously did a linear scan over all field IDs to find the matching entry. This PR implements binary search for locate_object_field when the Variant metadata's sorted_strings bit is set, which guarantees that field IDs within an object are sorted.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 481e42a and e0fe68d.

📒 Files selected for processing (1)

• cpp/src/io/parquet/experimental/variant_extract.cu

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📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved field lookup when reading variant data with sorted object fields.
  • Preserved support for unsorted object fields while maintaining validation for bounds and read failures.
  • Enhanced path resolution to interpret object metadata correctly.

Walkthrough

The change adds sortedness-aware object field lookup for Parquet variant extraction. Sorted field IDs use binary search. Unsorted field IDs use linear scanning. Path resolution reads sortedness metadata and passes it to the lookup.

Changes

Variant object path resolution

Layer / File(s)	Summary
Sorted-aware object field lookup and path wiring cpp/src/io/parquet/experimental/variant_extract.cu	locate_object_field selects binary search or linear scanning from is_sorted. Both paths validate reads and offset bounds. resolve_path forwards the metadata sortedness flag.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: vyasr, wence-, vuule

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the binary search optimization for Parquet Variant object field ID lookup.
Description check	✅ Passed	The description explains the binary search change, its sortedness condition, and the completed testing and documentation checks.

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[abigalekim]

/ok to test 3d840b7