Refactor to use MVCCStore with explicit timestamps

[bootjp]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @bootjp, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant architectural shift in the storage layer by fully embracing a Multi-Version Concurrency Control (MVCC) model with explicit timestamp management. This change standardizes how data is accessed and modified across various service adapters, ensuring that all read and write operations are consistently tied to specific timestamps. The underlying Hybrid Logical Clock (HLC) has been optimized for better concurrency, and the removal of legacy storage implementations streamlines the system towards a unified, MVCC-centric approach.

Highlights

• MVCC Store Refactor: The core storage layer has been refactored to exclusively use an MVCC (Multi-Version Concurrency Control) store, with all operations now explicitly requiring timestamps for reads and writes.
• Hybrid Logical Clock (HLC) Optimization: The HLC implementation has been updated to use atomic.Uint64 for timestamp management, eliminating the need for sync.Mutex and improving concurrency for timestamp generation.
• Adapter Integration: DynamoDB, gRPC, and Redis adapters have been updated to interact with the new timestamp-explicit MVCCStore interface, replacing older generic store methods with *At variants (e.g., GetAt, PutAt).
• Legacy Store Removal: Several older, non-MVCC store implementations (BoltDB, in-memory stores) and their associated tests have been removed, simplifying the codebase and consolidating storage logic.
• Protocol Buffer Updates: Protocol buffer definitions (service.proto, internal.proto) were modified to include an optional timestamp field (ts) in RawGetRequest and were regenerated with newer protoc-gen-go versions.
• List Management Refinement: List-related helper functions have been extracted into a new list_helpers.go file, and list operations within the Redis adapter now directly leverage the MVCCStore's timestamp-aware methods.

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[gemini-code-assist]

Code Review

This pull request is a significant refactoring that moves the system towards a proper MVCC architecture by introducing an MVCCStore with explicit timestamp management. This is a great improvement, simplifying the storage layer and making timestamp handling more explicit. The switch to a lock-free HLC implementation is also a notable performance enhancement. However, I've identified a critical issue in the transaction timestamping logic that could violate atomicity by allowing mixed timestamps within a single transaction. Additionally, there are a couple of high-severity race conditions in the Redis adapter where separate read operations within the same command handler do not use a consistent snapshot timestamp. Addressing these issues is crucial for the correctness and stability of the system.