HippoBaro opened a new pull request, #9831:
URL: https://github.com/apache/arrow-rs/pull/9831

   # Which issue does this PR close?
   
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   - Spawn off from #9653 
   - Contributes to #9731
   
   # Rationale for this change
   
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   See #9731
   
   # What changes are included in this PR?
   
   Represent definition and repetition levels as `LevelData`/`LevelDataRef` 
with `Absent`, `Materialized`, and `Uniform` variants, and thread this through 
Arrow level generation, CDC chunking, and the generic column writer.
   
   Uniform level runs, such as required fields and all-null pages, can now be 
encoded without materializing dense `Vec<i16>` buffers. Add bulk run support to 
`LevelEncoder`/`RleEncoder` so repeated levels are encoded in amortized O(1) 
after the RLE warmup, while preserving histogram, row count, null count, page 
splitting, and CDC chunk accounting.
   
   # Are these changes tested?
   
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   All tests passing. Coverage exercises bulk RLE level encoding, 
compact/uniform `LevelData` slicing and writer roundtrips across Parquet v1/v2, 
and CDC/Arrow writer behavior including all-null and nested-level cases.
   
   # Are there any user-facing changes?
   
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   None.
   


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