Query Performance Tracking & Message Handling Refactor

[ric-v]

This pull request introduces significant new features and architectural improvements focused on query performance tracking, enhanced explain plan visualization, and a robust message handling system. It also removes the legacy AI CodeLens provider and cleans up related code, streamlining the extension's interface and maintainability.

Major new features and improvements:

• Query Performance Tracking: The extension now automatically tracks query execution times and provides alerts if performance degrades significantly, with historical performance data and alerts surfaced in the UI. [1] [2] [3] [4] [5] [6]
• Visual Explain Plans: Enhanced support for visualizing EXPLAIN (FORMAT JSON) output, making query execution paths more understandable via improved graphical representations.

Architectural and codebase improvements:

• Message Handling Refactor: The internal message routing system has been refactored to use a MessageHandlerRegistry pattern. This brings improved stability, easier extensibility, and clearer separation of concerns for handling notebook/renderer messages. [1] [2]
• CodeLens UX Simplification: The AI CodeLens provider (AiCodeLensProvider) and its registration have been removed, cleaning up the notebook cell interface and focusing CodeLens actions on query-related features. [1] [2] [3]

Other notable changes:

• Changelog and Documentation Updates: The CHANGELOG.md and README.md have been updated to reflect the new features and improvements, ensuring users are aware of the latest capabilities. [1] [2] [3]

These changes collectively improve the extension's performance insight capabilities, user experience, and code maintainability.