add: annotate stage logic

[liurt1218]

No description provided.

[Copilot]

Pull Request Overview

This PR adds functionality to automatically annotate ML training stages in source code by detecting method calls like train(), eval(), save(), etc. and inserting corresponding annotate_stage() calls.

• Implements stage detection logic using tokenization to identify training, testing, and checkpointing patterns
• Adds automatic import insertion for annotate_stage function
• Integrates stage annotation into the existing instrumentation pipeline

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