feat!: Add get_parquet_schema API to ParquetHandler

[DrakeLin]

What changes are proposed in this pull request?

Adds a new get_parquet_schema method to the ParquetHandler trait that reads the Parquet file footer to extract the schema.

• Implemented get_parquet_schema for SyncParquetHandler (synchronous file system reads)
• Implemented get_parquet_schema for DefaultParquetHandler (async with object store and presigned URL support)

How was this change tested?

Unit tests testing we can read checkpoint schema

[codecov]

Codecov Report

❌ Patch coverage is 77.61194% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.68%. Comparing base (678f280) to head (ecb6d0c).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
kernel/src/engine/default/parquet.rs	75.67%	15 Missing and 3 partials ⚠️
kernel/src/engine/sync/parquet.rs	80.00%	7 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1498      +/-   ##
==========================================
- Coverage   84.95%   84.68%   -0.28%     
==========================================
  Files         121      122       +1     
  Lines       32603    32875     +272     
  Branches    32603    32875     +272     
==========================================
+ Hits        27699    27841     +142     
- Misses       3562     3675     +113     
- Partials     1342     1359      +17     

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