perf(storage): add binary checkpoint serialization prototype

Overview

FaultPlane requires efficient state movement for future distributed recovery scenarios.

This issue introduces a binary serialization prototype for checkpoint data.

Proposed Work

Implement:

• Binary serialization using MessagePack
• Checkpoint serialization tags
• Reusable byte buffers using sync.Pool
• Serialization benchmarks

Expected Outcome

Measure:

• Serialization speed
• Payload size reduction
• Memory allocations
• CPU overhead

Requirements

• Maintain backward compatibility
• Keep serialization layer independent from storage implementation
• Include benchmark tests

Notes

This prepares the foundation for future distributed checkpoint replication.

Start by locating the checkpoint data structures and the boundary between serialization and storage; the issue does not name specific files or entry points. Review how backward compatibility can be preserved, then add benchmark tests covering speed, payload size, allocations, and CPU overhead. Done means an independent MessagePack prototype with reusable buffers and reported benchmark results.