docs: Add comprehensive advanced topics (WAL and Compaction)

- Added Write-Ahead Log (WAL) documentation with durability guarantees
- Documented performance vs durability tradeoffs (19% reduction for zero data loss)
- Added sync modes (fsync, fdatasync, async) with use cases
- Included WAL monitoring, recovery, and troubleshooting
- Added File Compaction documentation for query optimization
- Documented 901x file reduction and 80.4% compression results
- Showed 10-50x query performance improvements after compaction
- Included configuration, monitoring, and best practices

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Co-Authored-By: Claude <noreply@anthropic.com)

Author: Ignacio Van Droogenbroeck