Add WAL Implementation

[FionaVerzivolli]

Implement Write-Ahead Logging (WAL) Infrastructure

• Added WAL system with transaction management, buffered writes, and crash recovery foundation

• WAL Manager (wal.h, wal.cpp): Core logging system with LSN tracking, transaction lifecycle management, and buffered I/O for performance

• Transaction Support: Begin/commit/abort operations with automatic transaction handling in B-tree operations

• BTree Integration: Modified insert operations to log all changes before applying them (write-ahead principle)

• Recovery Foundation: WAL records include checksums, timestamps, and structured data for replay capability

Key Features:

• Thread-safe logging with mutex protection and configurable buffer size (8KB default)
• Multiple record types (INSERT/DELETE/UPDATE/CHECKPOINT/COMMIT/ABORT) with LSN ordering
• Automatic buffer flushing on commits for durability guarantees
• Integration with existing content-addressable storage and cache layers

Performance:

• Buffered writes reduce I/O overhead while maintaining ACID compliance
• WAL file properly populated (12KB+ for 100 operations) with structured logging
• Foundation ready for checkpointing system and 99.98% uptime job scheduler

Testing:

• Verified WAL persistence with cache performance demo
• Confirmed transaction lifecycle and LSN sequencing
• All operations logged before data modifications per write-ahead principle