Improve Page struct

[Anthony4m]

• Add uniquely identifies a page in the database
• Add Page manger to handle the lifecycle of pages
• Add serialization support
• Add PageAllocator that manages free pages and allocates new ones
• Add PageBuffer that manages cached pages in memory
• Add RecordPage that specifically handles storing records
• Block navigation methods (NextBlock, PrevBlock, IsFirst)
• Deep copy functionality
• Comprehensive test suite
• Performance benchmarks
• Input validation
• Additional helper methods