feat: Add EXPLAIN query plan command

[aviralgarg05]

Description

Users have no visibility into how their queries are being executed or optimized by the AI engine.

Requirements

• Implement an EXPLAIN <query> command.
• Output should show:
  • The parsed SQL structure.
  • Whether the result was served from cache (and the cache similarity score).
  • The execution path chosen by the RL agent (with Q-values if possible).

Impact

• Critical for debugging and understanding AI optimization decisions.

[samarjeet818]

Hi @aviralgarg05

I would like to work on this issue under OSCG26.

The EXPLAIN query plan feature will improve transparency and debugging in NexumDB, and I’m confident I can implement the required functionality (parsed SQL structure, cache status with similarity score, and RL execution path with Q-values).

Please assign this issue to me. I’ll begin working on it and share updates soon.

Thank you!