### PR details
feat: Add Excel export support and fix variable reference regex
Changes:
- Add Excel export output format option to Message component
- Apply nest_asyncio patch to handle nested event loops
- Fix async generator iteration in canvas_app.py debug endpoint
- Add underscore support in variable reference regex pattern
### What problem does this PR solve?
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
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Co-authored-by: Shivam Johri <shivamjohri@Shivams-MacBook-Air.local>
