Release v0.10.20 - Cost Analysis Division by Zero Fix

Bug Fixes:
- Fix division by zero error in unified cost analysis report
- Properly handle edge case when all stacks have $0 costs
- Improve average stack cost calculation logic

This fixes the error:
'float division by zero' that occurred when running:
thothctl check iac -type cost-analysis --recursive

on projects with multiple stacks having zero costs.