Integrate RoshenHysteresisModel into CoreLosses

- Move BHLoopCacheKey, BHLoop, and RoshenParameters structs to CoreLosses.h
- Move RoshenHysteresisModel class declaration to CoreLosses.h
- Move all RoshenHysteresisModel implementation (~735 lines) to CoreLosses.cpp
- Remove standalone RoshenHysteresisModel.h and RoshenHysteresisModel.cpp files
- Remove obsolete include from CoreLosses.cpp

The Roshen hysteresis model is now fully integrated into the CoreLosses module
for improved code organization and easier maintenance.

Author: AlfVII