enhance: add column-level writer policies

[jiaqizho]

Add shared writer properties for disabling per-column compression and statistics by column name. The new keys are exposed through the C++ API and C FFI as VECTOR_STR properties, with unknown column names warned once during writer initialization.

Apply the policies in the Parquet writer by disabling compression as UNCOMPRESSED plus plain non-dictionary encoding for configured columns, and by disabling statistics for configured columns while preserving the default no-statistics behavior for BINARY and FIXED_SIZE_BINARY.

Keep Vortex behavior unchanged in this pass: non-empty column policy properties log a warning and are ignored until Vortex column-level layout support is added.

[sre-ci-robot]

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This pull-request has been approved by: jiaqizho
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[codecov]

Codecov Report

❌ Patch coverage is 99.02913% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 74.99%. Comparing base (746f8b9) to head (56148fe).

Files with missing lines	Patch %	Lines
cpp/src/writer.cpp	96.42%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #537      +/-   ##
==========================================
+ Coverage   74.89%   74.99%   +0.10%     
==========================================
  Files         149      149              
  Lines       13935    14005      +70     
  Branches     2093     2105      +12     
==========================================
+ Hits        10436    10503      +67     
- Misses       3499     3502       +3     

Flag	Coverage Δ
cpp	78.12% <99.02%> (+0.09%)	⬆️
python	44.74% <ø> (ø)

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