Consolidate ArrowFileSource and ArrowStreamFileSource

This commit consolidates the separate ArrowFileSource and ArrowStreamFileSource
implementations into a unified ArrowSource with an ArrowFormat enum.

Key changes:
- Removed ArrowFileSource and ArrowStreamFileSource structs
- Added ArrowFormat enum (File, Stream) to distinguish between formats
- Created unified ArrowSource struct that uses ArrowFormat to dispatch
- Kept separate ArrowFileOpener and ArrowStreamFileOpener implementations
- Consolidated all FileSource trait implementations in ArrowSource
- Format-specific behavior in repartitioned() method (Stream returns None)

This consolidation reduces code duplication while maintaining clear separation
of concerns between the file and stream format handling.

Part of apache#18627

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Co-Authored-By: Claude <[email protected]>

Author: adriangb