fix: possible snapshot message size error and log info

[hzcheng]

Description

Please briefly describe the code changes in this pull request.

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

Hello @hzcheng, 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 focuses on improving the robustness and observability of snapshot operations. It addresses a potential issue with inaccurate snapshot message size calculations by refining the size determination logic to consider all data characteristics. Additionally, it enhances debugging by adding a detailed log entry upon successful time-series data snapshot reads, providing crucial information about the virtual group and data size.

Highlights

• Snapshot Message Size Calculation: The logic for calculating the size of block data within snapshots has been enhanced to accurately account for various data flags (HAS_NONE, HAS_NULL, HAS_VALUE) and variable data types, including their respective offsets. This change aims to prevent potential snapshot message size errors.
• Enhanced Snapshot Read Logging: A new debug log message has been introduced for successful time-series data snapshot reads. This log now includes the virtual group ID (vgId) and the total size of the read data, providing better visibility and debugging capabilities for snapshot operations.

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[gemini-code-assist]

Code Review

This pull request addresses a potential miscalculation of snapshot message sizes and adds a helpful debug log. The core change in tBlockDataSize correctly accounts for various column states, including nullability bitmaps and variable-length data offsets, which is a crucial fix. The new debug log in tsdbSnapReadTimeSeriesData will aid in monitoring and debugging. While the logic is sound, I've suggested a refactoring for the size calculation to improve its clarity and maintainability.