feat: Complete Code Coverage Analysis Integration with Tarpaulin

- Replace TODO stub with comprehensive tarpaulin integration
- Add real coverage analysis with JSON output parsing
- Implement per-crate coverage tracking and reporting
- Add quality gates with 80% threshold enforcement
- Support XML/HTML/LCOV output formats for CI integration
- Include fallback mechanisms when tarpaulin not available
- Add comprehensive test coverage for all functions
- Generate detailed coverage reports with uncovered lines analysis

closes #80

Author: milliondreams