CVRmap v4.2.0 - Parallel Processing Release

Major Features:
- Comprehensive parallel processing support for multi-CPU acceleration
- Chunked multiprocessing with intelligent optimization
- CLI integration with --n-jobs parameter
- Configuration file support for parallel settings
- 4-8x performance improvement on multi-core systems

Performance Enhancements:
- Parallelized delay mapping with chunked processing
- Parallelized CVR computation with GLM fitting
- Parallelized 4D regressor map generation
- Near-linear scaling with available CPU cores
- Memory-efficient processing with optimal chunk distribution

Technical Improvements:
- Added joblib dependency for robust parallel processing
- Standalone worker functions for proper serialization
- Environment isolation to prevent GUI backend conflicts
- Automatic fallback to sequential processing when needed
- Comprehensive logging for parallel operations
- Enhanced error handling in parallel workers

Documentation:
- Updated README with parallel processing usage examples
- Performance benchmarks and configuration guidance
- Complete CHANGELOG with technical details
- Docker image updated to v4.2.0