Add parallel property flash calculations with derivative support

[EvenSol]

Add parallel property flash calculations with derivative support

Summary

Adds high-performance parallel property flash calculations to ThermodynamicOperations, enabling 100+ simultaneous thermodynamic calculations using multiple CPU cores.

New Features

• propertyFlashParallel() - Parallel PT/PH/PS flash using all available cores or custom thread count
• propertyFlashBatch() - Memory-efficient batch processing for large datasets (100M+ points)
• propertyFlashDerivatives() - Returns both properties AND numerical derivatives (∂P, ∂T) in a single optimized call using central finite differences

Key Highlights

• Thread-safe execution via fluid cloning
• Supports single-phase, two-phase, and three-phase systems
• Configurable thread count and step sizes for derivatives
• Python-compatible (uses standard lists, no Java ArrayList needed)

Files Added/Modified

• ThermodynamicOperations.java - Core implementation
• PropertyFlashParallelTest.java - 17 unit tests
• docs/parallel_property_flash.md - API documentation
• docs/examples/parallel_property_flash_example.ipynb - Jupyter notebook with examples