fix: Fix parquet decode of plain pages in dictionary column

[nameexhaustion]

• Fixes Cannot read plain encoded pages from Parquet for columns with an arrow dictionary type #28959

Autogenerated by Claude Opus 5.

[github-actions]

The uncompressed lib size after this PR is 60.3488 MB.

[codecov]

Codecov Report

❌ Patch coverage is 86.66667% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.37%. Comparing base (a6782fa) to head (b80fc63).
⚠️ Report is 99 commits behind head on main.

Files with missing lines	Patch %	Lines
...-parquet/src/arrow/read/deserialize/categorical.rs	86.66%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #29001      +/-   ##
==========================================
- Coverage   81.58%   81.37%   -0.22%     
==========================================
  Files        1890     1886       -4     
  Lines      268762   267155    -1607     
  Branches     3264     3061     -203     
==========================================
- Hits       219280   217391    -1889     
- Misses      48637    48986     +349     
+ Partials      845      778      -67     

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