Extract compaction logic to Compactor class (SOLID)

[abdellatifLabr]

Summary

• Extract compaction logic from Database class to a new Compactor class following Single Responsibility Principle
• Created src/jsonldb/compactor.py with Compactor class
• Database.compact() now delegates to Compactor.compact()

Changes

• New file: src/jsonldb/compactor.py with Compactor class containing:
  • _merge_records() - merges data file records with WAL entries
  • _write_compacted_records() - writes compacted records to temp file
  • _rebuild_indexes() - rebuilds main and field indexes
• Modified: database.py - imports Compactor, delegates compact() call
• Not exported: Compactor is internal-only (not in public API)

Benefits

• Database class has one reason to change (database operations)
• Compactor class has one reason to change (compaction logic)
• Easier to test and maintain