## US Data Source Optimization

### Problem
Describe the problem this PR solves...

### Solution
Fix Yahoo Finance limitations with FINNHUB fallback

### Changes
- List specific changes made
- Include performance improvements
- Mention any new features

### Testing
- [ ] Unit tests pass
- [ ] Integration tests pass
- [ ] Performance benchmarks included
- [ ] Documentation updated

### Breaking Changes
None - fully backward compatible

### Checklist
- [ ] Code follows project style guidelines
- [ ] Self-review completed
- [ ] Tests added/updated
- [ ] Documentation updated
- [ ] No merge conflicts

### Performance Impact
- Improved performance by X%
- Reduced memory usage
- Better error handling

### Additional Notes
Any additional context or notes for reviewers...
