refactor: Extract sort-merge join filter logic into separate module (#19614)

Refactored the sort-merge join implementation to improve code
organization by extracting all filter-related logic into a dedicated
filter.rs module.

Changes:
- Created new filter.rs module (~576 lines) containing:
  - Filter metadata tracking (FilterMetadata struct)
  - Deferred filtering decision logic (needs_deferred_filtering)
- Filter mask correction for different join types
(get_corrected_filter_mask)
- Filter application with null-joined row handling
(filter_record_batch_by_join_type)
  - Helper functions for filter column extraction and batch filtering

- Updated stream.rs:
  - Removed ~450 lines of filter-specific code
  - Now delegates to filter module functions
  - Simplified main join logic to focus on stream processing

- Updated tests.rs:
  - Updated imports to use new filter module
  - Changed test code to use FilterMetadata struct
  - All 47 sort-merge join tests passing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: viirya