feat: create enhanced CI/CD workflow combining best features from existing workflows

- Add concurrency controls to prevent overlapping runs
- Implement least privilege permissions for security
- Include auto-fix capabilities for formatting and clippy issues
- Integrate comprehensive security scanning (cargo audit, deny, secrets detection)
- Add performance benchmarking with hyperfine
- Maintain cross-platform testing with incremental builds
- Enforce 82%+ coverage threshold
- Provide detailed status summaries with modern GitHub Actions features
- Update README to document the enhanced workflow

This workflow replaces ci.yml and optimized-ci.yml with a more efficient and secure design.

Author: d-oit